[seizethecheese]

> We are strongly, strongly evolutionary oriented away from 'murder' - it's the original sin

The idea of sin is designed to fix less than ideal human tendencies. If anything, this being the biggest sin means murder is the most inherent bad trait of humans.

[samus]

It's just the sin with the greatest consequences since it invokes the wrath of the groups the person being killed belonged to. Unlawful killings challenge the authority of those who determine which killings are lawful and which aren't, therefore destabilizing societies that are more complex than a hunter-gatherer group.

However, most religions do more than just declare murder to be a sin. They usually aim to foster bonds between relative strangers as well. And values like the guest-host relationship are held to apply to all humans and even to sentient non-humans.