Comment by chongli

Morality is an evolved heuristic for solving social conflicts that roughly approximates game theoretical strategies, among other things. Morality also incorporates other cultural and religious artifacts, such as "don't eat meat on a Friday."

Ultimately, it comes down to our brain's social processing mechanisms which don't have the tools to evaluate the correctness (or lack thereof) of our moral rules. Thus many of these rules survive in a vestigial capacity though they may have served useful functions at the time they developed.