If this is true then how is murder, rape, cannibalism, etc. justified?
this is where you said it:
Well, whether any of those are good or bad depends on the society and its moral system.
So if a person is from a different country then murder is OK because of the moral structure or one's religious affiliation? You didn't say it in terms of me and you, obviously, but what you implied is that murder or any other sin's moral value is based upon the society and its moral system?
Al Quaida terrorists are extremists. They believe that crashing a plan e into the World Trade Center was a religious crusade and they would be eternally glorified for that action. If moral absolutes are not held then we as the victims can just say "Well, if its they think that's the right thing to do then we can't interfere." No, behavior has to have a moral structure (right and wrong). Evolution does not agree with this because our behavior would just be the way we evolved. Did Ed Gein evolve to go through with countless gruesome murders, did Mother Theresa evolve to do good, did Hitler evolve to be the leader of massacres? If there's not a benchmark for what is right and wrong then truth is truly lost.
on rape, murder, cannibalism:
Each of those could be said to have either an advantage or disadvantage as far as evolution would be concerned..
Just look at what you posted in response to my comments. From that perspective a "sin" (if you have morals) may have an evolutionary advantage over another. If this is true then carnivores such as lions, sharks, etc. are the same as murderers. Except that carnivores kill so they can live....Why do humans kill other humans? Does it benefit our existence? Carnivores kill because they have to and its instinct but humans function on a level of right and wrong. You don't have to be a scientists to see it.