I think of morality as being a complex system emerging from the interplay between the demands of individual self-interest and societal self-interest.

The parts of morality that emerge from individual self-interest are mostly fixed and not very controversial, based on common human desires - I would prefer not to be robbed, raped, or killed, and enough other people share those preferences that we can make moral rules against them and generally enforce them.

The parts of morality that arise from societal self-interest are more highly variarble, since what is good for a given society is very context dependent, and more controversial, since what is good for one part of society may be bad for another. In Aztec culture, human sacrifice was morally permissible, and even required, because it was a way of putting an end to tribal conflicts (the leader of the losing tribe would be executed, but in a way viewed as bringing them great honor, minimizing the chances of relatives seeking vengeance). In the American South, slavery used to be moral acceptable (because their plantation-based economy really benefited from it) whereas it was morally reprehensible in the North (because their industrialized economy required workers with levels of skill and education incompatible with slavery). Even with modern America, you see vast difference in moral views over guns, falling out along geographic lines (in rural areas gun ownership is fine, because guns are useful tools; whereas in urban areas gun ownership is suspect, because there's not much use for them except as weapons used against other people).