Cultural relativism about morality is not a popular academic position, but it is a position one hears in discussions with the “man on the street” when it comes to morality and ethics. Sometimes it is helpful to look at the consequences of certain views. The following example comes from Harry Gensler:
(CR) “The good” in morality is socially approved by the majority of the relevant society.
Now we should examine what would be true if (CR) is true. Let’s take this claim, for example:
(INF) The norms set up by my society about what is good couldn’t be mistaken.
At first glance, most people are inclined to reject (INF), even if they embrace (CR). If, as shorthand for (CR), we substitute the phrase “socially approved” for “good,” however, we will see (INF) is very nearly a tautology. It’s difficult to see how, if good is socially approved norms, that it could also be contrary to them. “So what?” you might think. “That’s an interesting fact about CR, but I don’t see a problem.” Consider the following argument:
1. If (CR), then (INF).
2. If (INF), then no moral progress is possible.
3. If no moral progress is possible, then the abolition of slavery in the American south did not constitute moral progress.
4. Therefore, if (CR), then the abolition of slavery was not moral progress.
We’ve already defended (1) above, (3) is true by definition, and (4) is an entailed conclusion. (2) is a crucial premise, but it too can be defended. (INF) stands for “infallibility,” because it means that the moral norms reached by a society cannot be mistaken (though people could be mistaken about what the social moral norms are, it nonetheless follows that if, in reality, there is some particular social moral norm, on CR, it cannot be incorrect). Supposing (CR) to be true, imagine a moral reformer (like Wilberforce in England) crying out against the morality of slavery. It’s not just impractical, or annoying, or the like: it’s morally wrong! Yet, Wilberforce would just be mistaken, just as much as the man who insists that his favorite TV show is the correct favorite TV show to have. Now, certainly, moral change is possible, in that all it takes is Wilberforce changing the minds of the people, and a new social norm forms. But it is still not anything like moral progress. It’s really more like fashion sense. In moral progress, we (as individuals or societies) move away from activities that are wrong and move to those that are right (or so we hope). We don’t think, for example, that slavery is wrong now, but it was perfectly acceptable back then. We really believe that slavery was a shameful spot on our country’s history, and that it should not have taken place. We believe the moral reformers were morally praiseworthy. In short, we really believe we made moral progress.
Moral progression means moving closer to that objective moral standard. If that is the case, what is your objective moral standard? We have seen it cannot be culture. For if we embrace moral progress, it follows by modus tollens that we reject (CR)—and, incidentally, (INF). It seems the best explanation of morality is an objectively existing God.
 Harry J. Gensler, Introduction to Logic, 2nd ed. (New York: Routledge, 2010), 40.
 Ibid., 41.
 A further argument can be made that, depending on particular norms, Wilberforce, in our example, would actually be the one in the wrong, morally. This is because society may (in our example) plausibly have taken it that having slaves forcibly removed from them (that is, the government forcibly ending slavery) violates a fundamental moral right to slavery, so that Wilberforce would be advocating for that which was morally wrong. It wouldn’t matter that he would eventually be vindicated—on (CR), he was just morally wrong, and so blameworthy. This counterintuitive notion is laughable, but it’s all the more reason to reject (CR).