What would such a disagreement amount to?
Does it make any sense to say that they could not have been mistaken about the morality of these actions?
Cultural relativism also has the peculiar conse- quence that social reformers of every sort would always be wrong. Their culture would be the ulti- mate authority on moral matters, so if they disagree with their culture, they could not possibly be right. If their culture approves of genocide, genocide would be right, and antigenocide reformers would be wrong to oppose the practice. In this upside- down world, the antigenocide reformers would be immoral and the genocidal culture would be the real paragon of righteousness. Reformers such as Martin Luther King Jr., Mahatma Gandhi, Mary Wollstonecraft (champion of women’s rights), and Frederick Douglass (American abolitionist) would be great crusaders—for immorality. Our moral experience, however, suggests that cultural rela- tivism has matters exactly backward. Social reform- ers have often been right when they claimed their cultures were wrong, and this fact suggests that cul- tural relativism is wrong about morality.
Where cultural relativism holds, if you have a disagreement with your culture about the right- ness of an action, you automatically lose. You are in error by definition.