Another way to make the point, when you hear people solemnize about the relativism of values, is to find a value they cherish and excoriate it. This is a useful approach because most of the time, when people deny absolute morality, they are engaging in a rhetorical strategy in order to undermine some particular moral belief you hold and they don’t. Social liberals, for example, often discuss topics like drugs, pornography, and prostitution by saying, “How can you impose your beliefs on me? Who is to say what’s right?” They seem to be denying absolute morality. If they are not self-aware, they might even believe this.
So the way to call their bluff and expose their relativism as purely tactical is to insult the moral values they cherish. For example, you could say, “I don’t know why we have laws outlawing racial discrimination and gay-bashing. How can people presume to legislate morality?” Or “I am surprised people object so strongly to the Confederate flag. I don’t have a strong view one way or the other, but since morality is relative, can anyone really say that the South’s cause was wrong?” Or how about “What’s the big deal about the environment? Why should I preserve the planet for the sake of future generations? What have future generations ever done for me?” Say these things as if you believe them, even if you don’t.
Before you are finished, I think you will find your relativist up in arms, insisting that prejudice and racism are immoral and unjust, and that we ought to have laws restricting them and protecting the environment. The person who affirms these doctrines is not saying that his views on bigotry and environmentalism are simply a matter of personal preference. He is implying that everyone should feel this way, and no decent person should behave in a manner contrary to his principles. He may ignore the moral law in the way he acts toward you, but he is quick to invoke it as a standard for how he expects you to act toward him. In short, his actions confess that despite his loud denials, he too espouses morality as an absolute.