Normal procreation is found in every species. Homo-mania is found in only one. Which one seems unnatural now? Yep. The same one as before.
(Dolphins have been known to murder their own kind. Does that make it normal and acceptable for Mankind?)
In many species, the "new guy" will kill the young of the previous guy.
In many species, the mothers of the young will eat them if they become stressed or fearful.
In some species, both parents will eat their young when starving, or just because they want to.
In some species, only the two leaders are allowed to mate and have young.
In some species, an animal with the wrong coloration is not allowed to join or remain in the group.
If animal behavior is used to excuse human behavior, there really are no limits...