It depends on the circumstances. We don't kill animals because we are hungry. We kill animals because we want more enjoyment from food. If you are somewhere starving and it's you it the rabbit, go for it. That's not the common situation though.

Euthanasia is a much more complicated topic and I find it bewildering that we are focusing on this discussion on babies. I assume it's out of some notion of protecting the adorable innocence. I think it's important with these topics to try to keep emotions out of it because they just reflect biases we have built in due to evolution. Evolution of course is not your friend. Especially not after you've procreated.