Lions, for example, commit infanticide on a regular basis because they want to make sure that the little offspring that is being raised by the lioness is their own and not someone else's. Morality is an invention of human beings. It's a very good invention. I'm not suggesting we should abandon morality. I'm not suggesting, more to the point, that we should abandon ethics.
Ethics is a perfectly valid way of thinking about things.
We can all agree as a society that there are things that are wrong and things that are good. We can act on them, and we can enforce those things, but there is no higher power or no higher reason to tell us that this is right or this is wrong. I would really like for somebody to come down from the sky and tell me what is right and what is wrong. My life would be much, much easier. Unfortunately, that doesn't happen.