Why should religious belief or freedom be a defense against a killing?

If I stomp you to death because my church says yours is a depraved, child-molesting bunch I am just as guilty of the killing as I would be if we sat in the same pew. If I burn hundreds of "heretics" to death on a huge pyre after they surrender to me, I am guilty of murder. If I cause the death by starvation of thousands who won't convert to my religion before I give them a bowl of soup I am guilty of murder. If I kill the food source for an entire people so I can force them under my control, I am guilty of murder.