What you seem to be suggesting here is that people just really want to kill others really badly, and are eager to find an excuse to do it. I don't happen to view humans so basely.
I contend that the Bible or other religious texts can in fact be a source for a person's violent actions, not merely an excuse for it. This would seem to be an attempt to whitewash the Bible or other religious texts of calling on their followers to kill in the name of their God. If you read through the Bible or other religious texts, you will find described as punishable by death things which we would today consider rather mundane practices. Your children misbehave?
(And as an aside, what exactly led us away from this sort of thinking? Was it God suddenly deciding that practice was no longer morally 'correct,' or was it secular morality forcing religion to abandon such dogma? And if it is a God who decides it is moral one day to kill your children if they misbehave and immoral the next, you have yourself but an arbitrary designation of morality that is not consistent nor has any self-correcting mechanism for determining what is moral.)
Consider the case of regular people who are convinced by their religion to kill. When a woman kills her children because she believes God told her to do so, is that her using religion as an excuse for her secret craving to murder? Just some regular housewife, who thinks God told her to do it. I think religion is directly responsible for this woman's behavior--it is like poison to a rational mind. How could she rationalize that her children should be killed? Surely the story of Isaac, something this woman would certainly be aware of, has more to do with it than some insatiable appetite to kill?
Can you really say the intent to kill is truly independent of what some religion may convince a person is the right thing to do?