1. There are really very few bona fide moral relativists. Not that I’m suggesting that the rest are acting mala fide. But a real moral relativist, an actual specimen of the no-I-mean-it-there-really-is-no-such-thing-as-good-or-evil, is hard to find but easy to flush out and dispatch. If you think you’ve actually met one, and he lets slip the refrain that “It’s all relative,” then brandish your blackjack and reply, “Precisely. Now hand over your wallet, and know full well that I’m going to hit you anyway because I like the thuddy sound.” If he merely sighs and takes his self-prescribed medicine, then he is genuine.
I myself have never met a real, down to the bone and all the way into the marrow moral relativist, and their very rarity is our first sure sign of why moral relativism makes no sense.
2. Much moral relativism results from intellectual confusion, rather than bad faith. People see that there are major disagreements throughout history among different peoples about what exactly is moral and immoral. For example, it was perfectly moral to destroy your unwanted children in ancient Rome; in fact, it was demanded of fathers, by the famous Twelve Tables, that they destroy any deformed children. Christianity denied that this was moral and hence denied the Roman moral code. When Christianity became the foundation of society after Rome crumbled, abortion and infanticide were considered immoral. Well, now things have come around again, and we’re back to pagan Rome.
But the fact that there is disagreement does not mean that morality is completely relative. That makes no sense. In no other area do we take initial disagreement as a sure sign of defeat. The fact of disagreement is the starting point from which our moral inquiry naturally begins, and the problem it attempts to clear up through investigation. That is why Aristotle, the first great moralist, begins his book on ethics with the fact that people disagree morally, and ends with how they really should think and act morally.
3. Moral relativism is often merely a thin disguise donned by moral revolutionaries, and contradicts their own moralistic modus operandi. So, for example, Marx declared that all morality was merely a reflection of the modes of production in the society in which it occurs, and then spent long hours detailing the injustices of capitalism to make his case and outlining the lovely harmoniously just society (where everyone is cheerfully giving and taking according to ability and need) that would spring up once the dictatorship of the proletariat had scrubbed the world clean of the bourgeoisie.
But this was and is nonsense. The felt moral outrage at injustice and the deep desire for utopian justice that animated Marx, even though they were distorted by his ideology, were quite natural and real and universal at their source. That is why he could so effectively use them to incite indignation in his readers. The desire for justice and the hatred of injustice are fundamentally human. Marxism became powerful, not to mention so hideously destructive, precisely because he could count on these human moral fundamentals as real rather than mere side-effects of economic relationships.
4. Moral relativists are strangely selective about their relativity because actual consistency would make nonsense of their position. Sexual revolutionary Alfred Kinsey pulled off his normalizing of sexual deviancy by arguing that (for example) homosexuality and “inter-specific matings” (i.e., sex between members of two distinct species, the equivalent of bestiality) regularly occur among animals. Since we are merely animals too, so he argued, then homosexuality and bestiality must be natural—and hence not immoral. But on this logic, anything that appeared with fair frequency among animals—such as cannibalism and sexual brutality—would be natural, and hence moral, for human beings.
5. As a way of summing it all up, we witness the most obvious and profound reason why moral relativism makes no sense: aside from the rare exception mention in No. 1 above, there is almost invariably a fundamental contradiction between what the moral relativist says and what he does. Whatever a man says about there being no right and wrong, when someone demands that he empty his wallet—be it a thug or IRS agent—he will treat it as robbery, a real injustice, rather than a mere transfer of funds.