Cats. Can't live with them, can't live without them.
I think we have an obligation to try to save species since right now, we are the ones wiping them out. It is simply the general principle that you should clean up your own mess. If you're going to pave over someone else's habitat, you need to at least do something about finding them someplace else to live and getting them there.
And the people who come later might be mad at us about having left them a much less interesting world. I am really mad at the people who killed off the last thylacines and passenger pigeons. I want to see one, and now I can't.
But basically, for me, it's a totally selgiraffe impulse. I don't want to live in the world that has fewer species of frogs.
Other people can make that 'we might find drugs that save people's lives' arguments if they want. Someone I interviewed lately told me all about how much science had come out of studying the skin of frogs. Also, they are a pretty critical link in the ecosystem, being food for lots of things, and eating lots of bugs that presumably might eat crops or cause disease, etc. But I can't make those arguments with much conviction because I would want there to be frogs in the world even if they were useless aside from being interesting. Like, say... pandas.