Even if you are fine with line of reasoning you should consider the situation where we find ourselves in some fututre predicament where we have a disease that can only be cured by something we would synthesise from a rare protein that has only ever been found in the tears of the lesser Peruvian Fruitbat but unfortunately it's extinct and that's pretty much that.
Even if you don't buy the argument that we are custodians of the earth and its natural resources for future generations, extinction is a one-way door[1] and it's really not possible to say that allowing an animal to become extinct would serve our interests because we can't see the future to know how this may harm us in the future.
[1] Pretty much. Yes I know about the attempts to bring back the mammoth etc.
I think there's a relationship between human flourishing and animal extinctions. Human flourishing goes up as animal extinctions go up, but quickly reaches diminishing returns as more animals go extinct. I agree that we may have gone too far, but I also think that aiming for zero animal extinctions is severely limiting.
You're using this "Lesser Peruvian Fruitbat or whatever" as a rhetorical tactic to make environmental concerns seem silly, but we live on the same planet that they do. It's useful to consider extinction rates as a function of general environment health. If the water is so full of shit that the things living in it are dying, that's a good sign that the water isn't going to be good for us either.
