I'm coming around to the opinion that we should let the Earth be the Earth. By that I mean, when it's time for a species to go extinct, there's not much we can do to stop it, and probably not much reason to try. Species go extinct all the time, and not all of them from human causes. It's the way Nature works. I've got nothing against snail-darters, but does jumping through hoops and spending huge amounts of money to preserve them really help anything?