[donw]

Right, so the Samurai, who would randomly cut the heads off of people they didn't fancy, knew they were doing something wrong, and yet were totally okay with it? Beheading a few peasants was, after all, the right way to test out a new sword... there's even a term in Japanese for it: Tameshi-giri.

Plenty of societies, both ancient and modern, have legalized, or even encouraged, what we define as 'murder'.

And note that I'm not arguing that murder is acceptable; rather, that the definition for it changes so much between societies as to make the statement "Murder is wrong in all human societies." a completely meaningless phrase.

A likely explanation for the prohibition against the killing of other humans is strictly pragmatic: Societies where members can kill each other freely will self-destruct. This has nothing to do with 'murder being wrong', as much as free homicide not being a very stable evolutionary path.