Is murder intrinsically wrong?
Or is it wrong because it is in our self-interests? Because of the concept of reciprocity (if I murder someone, that must make it okay to murder me)?
The latter. After all, for some other species murder might not be a serious crime at all; some alien hive species for example might consider it more akin to vandalism. There’s no such thing as “intrinsic” morality - although we can usually act as if there was, since we all belong to the same species.
I apologize for repeating myself, but there is an additional reason, coming from our animal origins and the instincts of social species. We are instinctively attuned to our fellows, and the sight of a dead person (especially a member of our social group) is inherently discomforting to us. It’s how we’re “wired,” so to speak. Our laws and moral codes are, in part, based upon this instinctive framework. Much of what we hold to be “good and evil” stem from these instincts. Sharing, cooperation, trust, respect, and love are all, in part, instinctive human behaviors.
That sort of speaks to the concept of does God exist.
To leave that aside, I think it’s not necessarily the “it must make it okay to murder me” thing. People have no problem doing unto others what they wouldn’t like being done unto them, but I think it is more for shared benefit.
Sure it would be nice if I could kill the neighbor and take all of his stuff, but then I would have to sit up at night and make sure that the next neighbor didn’t come and take my stuff and kill me. Everyone is distrustful and on alert, split into warring factions and groups for mutual benefit. Isn’t it better if we can all relax and have all of society try to put a stop to these murders?
This is the foundation of law. Sure, I would like to be able to drive 110 mph on the freeway, but I don’t want you doing it. You want to do it, but don’t want me to be able to do it. So we all have to agree that nobody can do it.
Even animals don’t commit murder. They kill for food and defense, although I guess they fight to the death sometimes over mating. Murder requires understanding of intent and right and wrong, so human society feels unease and guilt unless it can be justified. Unfortunately historically humans have had an easy time making up justifications. But I never heard of any society modern or ancient comfortable with the idea of letting the average citizen commit murderer. That would be anarchy or chaos.