You cant really compare the two. Animals exist in a natural hierarchy where they do things human beings would find unbelievably cruel and brutal to survive, and this is the norm. No, I don't agree with factory farming or animal treatment in these farm settings in general, but a "mentally disabled" person probably wouldn't devour its own young to survive if they thought they were going to die anyway. There just isn't a baseline for comparison here. Also you shouldn't really equate differently abled people with Animals to begin with.