Morality writ large is much harder to fix at the global level. Our sense of right and wrong comes from ourselves, meaning those around us but it doesn't answer the question of where those opinions of others comes from. And as you point out, there can be cultures where it's okay to kill people. In fact, it's considered admirable and heroic and for all kinds of reasons.
Matt Ridley talks with EconTalk host Russ Roberts about his latest book, The Evolution of Everything. Ridley applies the lens of emergent order to a wide variety of phenomena including culture, morality, religion, commerce, innovation, and consciousness.