The problem is that without the other life there can be no human life. We are on the top of the food chain and as such we depend on all other animals for our survival. Hopefully it makes sense what I'm saying.
oddly enough some climate scientists (james lovelock, in this case) take it as a given that most animal life is already doomed, and that humans will have to engineer a food source in order to survive. green goo might be in your future