The very notion of protecting "endangered" species goes against nature. If they can not adapt and evolve to the world they live in then they no longer are fit for survival. Look at Pandas, they absolutely refuse to -blam!- and repopulate. Why should we bother trying to help a species that doesn't care about themselves?
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The thing is most of them are endangered because of us. Polar Bears are losing ice and are drowning cause of us. Tigers are getting hunted down because of us. Your idea of if the animals can not adapt then they are not fit is true. But it's also true that we as humans could wipe them out regardless. I think it's far for them to at least get killed off on an even playing field until they evolve enough to the point where they can stand a chance against humans.