Please turn to Genesis 1, verse 11. If you have worked with animals, you have some understanding of the realm of midbrain responses. Within the midbrain, there is a powerful God-given resistance to killing your own kind. It comes inherently to humans as the spirit in man.
Every species, with a few exceptions, has a hardwired resistance to killing its own kind. In territorial and mating battles, when animals with antlers and horns fight one another, they head butt in a harmless fashion. I am sure it hurts but it is not lethal. But when they fight with other species, they go to the side to gut and gore. Piranhas will turn their fangs on anything but they fight one another with flicks of a tail. Rattlesnakes will bite anything but they wrestle with one another.
Almost every species has this hardwired resistance to killing its own kind. And when we humans are overwhelmed with anger and fear, we slam head-on into that midbrain resistance that generally prevents us from killing. Only sociopaths, who do not have that resistance, lack this innate violence immune system.
