I'd say it still comes down to the reason, honestly. I wouldn't blame anyone who was fighting in a war or someone who killed in self-defense, but outside of things like that, it becomes kind of a slippery slope.

Like, let's go back to this moon example. If the man who killed the other man with a rock did so because the victim had gone on a murderous rampage beforehand, I'd say it was probably justified. But if he was killed because he made a pass at the other man's significant other... well, that's too much.