I agree about the Arab cultures being stuck in time. I've called that the medievalism factor, and as Sam Harris stresses, it's largely a matter of their religiosity.

But don't you think the illusion of regulating war does threaten domestic tranquility? If you outlaw an act in one context (murder), and legalize it in another (war), you're in danger of giving the lie to the entire legal enterprise. If, as you say, moral and religious symbols are rationalizations of Darwinian realities, you still need to maintain the illusion that the the symbols aren't just frauds. A flat contradiction between laws threatens to bring down the incoherent culture.