An 'endangered species' is a population of organisms (either plant or animal) which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or through being directly killed by other species (including humans). Many nations have laws offering protection to conservation relevant species: for example, forbidding hunting, restricting land development or creating preserves. 'Biodiversity' means the variety of bacteria, plants, and animals that live on our planet. This includes the unique behavioural patterns and activities of each species. Biodiversity is an ecological concept discussed in many scientific circles. Many debates about biodiversity will ultimately boil down to how important this diversity is, either for its own sake, or for some specific human benefits.
Protecting endangered species helps protect humans: Humans actually benefit in a large number of ways from the protection of endangered species and thus continuing biodiversity. Firstly, the diversity of life and living systems is considered by many scientists to be a necessary condition for human development. We live in a world built on a carefully balanced ecosystem in which all species play a role, and the removal of species from this can cause negative consequences for the whole ecosystem, including humans. There is also the potential for almost any species to hold currently-unknown future benefits to humans through products they could provide. One example of this is the scrub mint, an endangered plant species which has been found to contain an anti-fungal agent and a natural insecticide, and thus holds great potential for use that benefits humans. Endangered species have also been known to hold the key to medical breakthroughs which save human lives. One example of this is the Pacific yew (a tree species) which became the source of taxol, one of the most potent anticancer compounds ever discovered. Biodiversity also helps protect humans in that different species' differing reactions to ecological problems may in fact act as a kind of 'early warning' system of developing problems which may one day negatively affect people. This was the case with the (now banned) dichlorodiphenyltrichloroethane (DDT) pesticide, as the deterioration of the bald eagle and the peregrine falcon through their exposure to DDT in fact alerted humans to the potential health hazards of this pesticide, not just to animals but also to humans. Thus the preservation of endangered species helps to protect humans, as this means plants and animals continue to play their specific role in the world's ecosystem which humans rely on, can act as an 'early warning' for problems which may affect humans, and may hold the key to scientific and medical breakthroughs which can greatly benefit humanity. Al this could be lost through the careless extinction of plant and animal species.
This argument fails to take into account the costs of protecting endangered species and weigh them against the potential harms of them becoming extinct. In a world where only 5% of plant species have been surveyed for their potential medicinal value, this means protecting the survival of the other 95% purely for the potential value that only a fraction of them may possess. All of this means denying development human development now, by not opening areas up for agriculture or not constructing housing. These are very real costs which impact upon peoples' lives, and may even outweigh those scientific and medical advances which may or may not be found in currently endangered species.
An environment with a great diversity of plant and animal species in it can act as a source for art and entertainment, enriching the lives of humans. Thus the preservation of endangered species is an important part of ensuring this diversity continues to exist so people and enjoy and be inspired by the many varied kinds of life on this earth. A good example of this is the re-introduction of the grey wolf into Yellowstone Park in the United States (where it had previously become extinct due to human action), which added to the biodiversity of the region and caused a greater influx of tourists into the park. People enjoy being surrounded by different kinds of nature, and so protecting endangered species is an important part of protecting human enjoyment.
The problem with this argument is that it prioritizes the enjoyment of some individuals over others with no real justification. The grey wolf, for example, went extinct in the Yellowstone region in the first place because humans considered it a pest and a threat to livestock and so hunted it to extinction. Clearly these people didn't enjoy the 'diversity' the grey wolf provided. We don't usually give something the force of law regarding animals just because some people enjoy it. For example, the UK has now banned fox hunting even though a great many people found it to be a source of pleasure and recreation. If everyone desired the protection of all endangered species, there would be no need for this law, but the fact that a law is needed to restrain human action shows that not everyone 'enjoys' this biodiversity in the same way.
Human moral responsibility to other species: Humans are unique and unprecedented in life on earth in that their intelligence and sentience far surpasses that of any other species ever known to have existed. Humans are not simply forced to kill or ignore other species by instinct alone, as other species are, but rather can make a variety of choices based not only on information but on moral grounds. Thus with our greater power comes a greater responsibility to act in a moral fashion, and not simply to prioritize our own human good over that of other species. The ability of animal species, for example, to feel pain and suffering is something we should consider and try to avoid, as we recognise that pain is bad for ourselves, and thus must be bad for animals as well. Similarly if we believe our own survival is a good thing, we should recognise that the survival of other species is also a moral good, and act accordingly to protect endangered species.
Superior human intellect and sentience only means that we should make sure we consider the moral ramifications of our actions, not that we should take any particular action as a result. It is entirely in keeping with this for us to conclude that human life and enjoyment are more important than animal life and species survival, and so for us to decide not to protect endangered species when this (as it by definition always will) infringes upon human benefits and enjoyment.
Human moral responsibility to future generations: Species extinction is an irrevocable occurrence. Outside of the film 'Jurassic Park', extinct species cannot be summoned back from the grave once human action has put them there. This means that when a current generation makes the decision not to protect an endangered species and thus allows human action to drive it to extinction, this denies future generations the ability to make up their own minds about the pros and cons of the survival of that endangered species, especially considering that they might want that species to exist for the aforementioned scientific, medical, aesthetic or moral reasons. For example, there is a great modern-day interest in the dodo species of bird which was hunted to extinction in Mauritius in the 17th Century. The opinion of many in the modern world today is one of regret at the bird's extinction and that it should have been protected, but a lack of consideration of the wishes of future generations in the 17th Century has meant that the humans of the 21st Century are denied the ability to decide on the value of this species themselves. Because we place a moral value on the ability of humans to make decisions (as we consider it to be a good thing when we ourselves have this ability) we should recognise that the possibly differing opinions of future generations should constrain our choices somewhat, and we should protect endangered species so that future generations can decide for themselves regarding their value.
By this argument, no human generation could ever decide that protecting a species is more trouble than its worth and so let it become extinct, as there would always be the theoretical possibility of a future generation that might regret this choice. Every choice we make as a generation constrains and widens the choices available to future generations. If we protect endangered species and therefore limit agricultural and housing land (to protect their environments) we deny future generations more plentiful food supplies and better housing. We may even deny the existence of more humans in the future by not having enough food to feed a population which could grow faster if the food supply was greater. We cannot allow the remote possibility of future regret to cause us to take actions which a great many people will 'regret' in the present.
Protecting endangered species can harm humans: Protecting endangered species by definition means restricting activity that humans would otherwise want to do, be it by turning woodland into farmland, turning meadows into housing developments, or by preventing us from eliminating 'pest' species which kill livestock or damage crops. For example, the reintroduction of the grey wolf into Yellowstone Park has increased once more the risk to livestock in the region and caused economic harms to ranchers there. Some of these species may even pose a threat to human lives, which may have been why they were hunted to extinction in the first place. In any case, less agricultural land and less land for housing can only mean higher food and housing costs (due to their decreased supplies in the face of a rising human population) for people, which has a detrimental impact upon human life.
 Bailey, Ronald. “Shoot, Shovel and Shut Up”. Reason.com. December 31, 2003. http://reason.com/archives/2003/12/31/shoot-shovel-and-shut-up
These possible harms can be outweighed by the gains we make as humanity from protecting these species. It is important to note that the way we benefit from protecting endangered species extends benefits not just to the current generation but to future generations in terms of the preservation of biodiversity for scientific and aesthetic reasons. By contrast, allowing farmers to hunt to extinction species which are a threat to their livestock is only a short-term gain which applies almost exclusively to the farmers themselves and not to humanity as a whole.
The practical difficulties of the 'endangered' status: The complications which have grown up surrounding the 'endangered' status given to some species are in themselves a good reason to do away with this cumbersome and harmful practice. It should firstly be noted that it can be incredibly difficult to get species removed from the 'protected' lists even once they have been added even when their numbers show they are no longer in jeopardy. The grey wolf again serves as a good example; it is considered to be 'endangered' (and thus protected) in the United States, as there are only 3,700 such wolves in the lower 48 States today, despite the fact that an estimated 58,000 grey wolves live in the wild in Alaska and Canada. This is clearly an example of a misapplication of the 'endangered' label but which is incredibly difficult to revoke once it has been given, due to pressure from ecological groups and the media.
The sort of laws used to 'protect' endangered species may even incentivize the exact opposite kind of behaviour on the part of landowners. When, for example, a farmer finds on his land an animal from an endangered species, and the law thus requires him to make significant changes to his farming practices to protect the creature, this imposes a significant economic cost on him. This means that that farmer may have a large economic incentive to simply dispose of the creature and hide the evidence of its presence, when in the absence of the law the farmer might not take any steps to intentionally exterminate all examples of that endangered species on his land. Economists writing in the Journal of Law and Economics found an example of similarly perverse incentives provided by endangered species protection law amongst logging companies in the United States. When faced with a protected species of woodpecker which preferred to nest in trees at least 70 years old, and which when found, the law required timber owners not to harvest wood within a large area around that woodpecker's nest, loggers simply responded by harvesting more trees in areas where these woodpeckers might appear and by intentionally harvesting tees at age 40 instead of waiting for them to mature to 70 and thus becoming potential habitats for the woodpeckers. This resulted in even less available habitat for the woodpeckers than before the protection laws were passed This example helps to further illustrate how 'protecting' endangered species requires cumbersome legislation that is prone to mistakes, difficult to retract and may incentivize even more harmful behaviour towards these species than if the laws did not exist.
 Bailey, Ronald. “Shoot, Shovel and Shut Up”. Reason.com. December 31, 2003. http://reason.com/archives/2003/12/31/shoot-shovel-and-shut-up
 Lueck, Dean, and Michael, Jeffery A. “Preemptive Habitat Destruction Under the Endangered Species Act”. Journal of Law and Economics. Vol. 46. No. 1. April 2003
This is argument for the reform of these laws, not against the laws themselves. Laws could also be introduced, for example, to require loggers to allow a certain percentage of their trees to reach the appropriate age for woodpecker nesting, or better review panels created to consider removing the 'endangered' label when it is no longer appropriate. These laws can shift as we see incentives shifting in order to ensure that good behaviour in incentivized overall.
Species extinction is a part of the natural world: Within evolution species naturally go arise and later become extinct as they struggle to adapt to changing environments and competition with other species. This be regarded as a part of the 'survival of the fittest' which drives evolution. Most extinctions that have occurred did so naturally and without human intervention. It is, for example, estimated that 99.9% of all species that have ever lived are now extinct, and humans have existed at the same time as only a fraction of these species. Therefore it cannot be claimed that species going extinct will somehow upset the delicate natural balance or destroy ecosystems. Ecologists and conservationists have in fact struggled to demonstrate the increased material benefits to humans of 'intact' wild systems over man-made ones such as farms and urban environments, which many species simply adapt to. Therefore any claims that humans causing the extinction of other species are somehow acting 'un-naturally' or 'immorally' or that they are risking ecological collapse as a consequence are mistaken, as they fail to understand that extinction occurs as a natural fact and that ecosystems adapt accordingly. No other species acts to prevent species besides itself from becoming extinct, and therefore again allowing another species to die out is in no way 'un-natural.'
 Raup, David M. “Extinction: Bad Genes or Bad Luck?” W.W. Norton and Company. New York. 1991
 Jenkins, Martin. “Prospects for Biodiversity”. Science. 14 November 2003. http://www.sciencemag.org/content/302/5648/1175.abstract
Other species may allow species other than themselves to die out, but they fail to do this because they act purely based on instinct and their instincts do not dictate to them to save other species. Humans, however, are capable of acting for a far greater number of reasons and after more consideration. For example humans are capable of empathy with other species and understanding that their pain and suffering mirrors our own, and thus that we should prevent it on moral grounds. What makes humans special is that they are more thoughtful than any other animal, and thus the moral standards for our behaviour are much higher.
Why human rights always trump animal rights: It has already been established that laws protecting endangered species cause harm to humans by denying them the opportunity to engage in behaviour they would otherwise desire to do. The problem with this is that it elevates 'animal rights' to an equal plane with human rights and therefore restricts human life and happiness. This is wrong as humans enjoy superior mental faculties to animals and also have greater sentience, meaning that humans are aware of their pain, suffering and the opportunities denied to them (for example through laws restricting land development) in a way in which animals are not. As a consequence, we should cause humans to have less happiness in life in order to protect the lives of 'endangered species', as animals' lives, 'happiness' and suffering are less meaningful than that of humans.
This argument fails to note that states restrict human behaviour towards animals with the aim of protecting animals in many situations, not just that of 'endangered species'. For example the aforementioned fox hunting ban, which outlawed hunting foxes with dogs as it was deemed excessively 'cruel' to the animal, even though many people enjoyed the practice. This is done not only because humans are able to hold themselves to a higher moral standard than animals but also because animal suffering tends to produce a negative emotional response in many humans (such as amongst those who disliked the suffering of foxes in hunts and pushed for the ban), and thus we prevent human suffering by preventing animal suffering.
Ishwaran, N., & Erdelen, W. “Biodiversity Futures”, Frontiers in Ecology and the Environment, 3. May 2005 http://www.jstor.org/pss/3868449 ;
Wilcove, D. S., & Master L. L. “How Many Endangered Species are there in the United States?”. Frontiers in Ecology and the Environment, 3. October 2008. http://www.jstor.org/pss/3868674 ;
Kurpis, Lauren. “Why Save?” EndangeredSpecie.com. Copyright 1997-2002. http://www.endangeredspecie.com/Why_Save_.htm ;
BBC News “'More foxes dead' since hunt ban”. BBC News. 17 February 2006. http://news.bbc.co.uk/1/hi/uk/4724028.stm ;
BBC News “Dodo skeleton find in Mauritius”. BBC News. 24 June 2006. http://news.bbc.co.uk/1/hi/sci/tech/5113372.stm ;
Bailey, Ronald. “Shoot, Shovel and Shut Up”. Reason.com. December 31, 2003. http://reason.com/archives/2003/12/31/shoot-shovel-and-shut-up ;
Lueck, Dean, and Michael, Jeffery A. “Preemptive Habitat Destruction Under the Endangered Species Act”. Journal of Law and Economics. Vol. 46. No. 1. April 2003. http://www.jstor.org/pss/10.1086/344670?searchUrl=%2Faction%2FdoBasicSearch%3Ffilter%3Djid%253A10.2307%252Fj100232%26Query%3Dred-cockaded%2Bwoodpecker%2B%26Search.x%3D0%26Search.y%3D0%26wc%3Don&Search=yes;
Raup, David M. “Extinction: Bad Genes or Bad Luck?” W.W. Norton and Company. New York. 1991; (9) Jenkins, Martin. “Prospects for Biodiversity”. Science. 14 November 2003. http://www.sciencemag.org/content/302/5648/1175.abstract ...