Like it or not people are killers. Been killing since the caveman times and will keep it up for a while longer.

Religion of any shape or form is not why we are killers since we were killers long before  any religion was around.

We are also shitters pissers and  eaters .

We can't stay alive without killing.  Yeah that is correct  whether we kill a plant or an animal to eat.
Or a white blood cell kills off a germ.  All that is killing.

Religion or rules of behavior were designed to limit the killing so as not to destroy our selves with too much killing.