Violence of humans against humans, why?

And in the intervals between campaigns he washes the blood off his hands and works for “the universal brotherhood of man” with his mouth. Man is the Religious Animal. He is the only Religious Animal. He is the only animal that loves his neighbour as himself, and cuts his throat if his theology isn’t straight. He has made a graveyard of the globe in trying his honest best to smooth his brother’s path to happiness and heaven.

He was at it in the time of the Caesars, he was at it in Mahomet’s time, he was at it in the time of the Inquisition, he was at it in France a couple of centuries, he was at it in England in Mary’s  day, he has been at it ever since he saw the light, he is at it today in Crete. He will be at it somewhere else tomorrow. The higher animals have no religion. And we are told they are going to be left in the Hereafter. I wonder why? It seems questionable fate.