Yes, there is diversity of moral practice, but there is much less diversity of moral standards. One group may permit one wife and another group four or more wives, but all groups agree on the indispensability of the family and its moral obligation to provide for the young. James Q. Wilson’s book The Moral Sense makes the case for a universal grammar of morality rooted in our human instincts. Donald Brown’s study Human Universals reveals more than three hundred unvarying patterns of behavior, including a host of moral beliefs that are shared by all known cultures.” To take two of his examples, various cultures may specify situations in which it is morally permissible to lie or act in a cowardly manner, but in no culture are dishonesty and cowardice upheld as virtues.
What, then, are we to make of relativism—the influential doctrine that says that morality is relative? I agree that relativism has something going for it, in that people even within our own society disagree about the content of morality. There are also debates about the priority of one moral principle over another. Different individuals and even societies disagree over how a moral principle should be applied in a given situation. But on the existence of moralstandards there is no disagreement. Consequently relativism of moral belief and practice in no way invalidates the claim that morality is absolute. Indeed I submit that not only is morality absolute, but everyone, including self-proclaimed relativists, knows that it is absolute. Relativism in its pure sense simply does not exist.
If you are confronted by a relativist who insists that all morality is relative, go ahead and punch him in the face. If he does not respond, punch him again. At some point he will protest, “That’s not right. You shouldn’t have done that.” Then you can explain to him that your actions were purely educational. You were simply demonstrating to him that even he does not believe his relativist doctrine. His objection was not “I don’t like being punched” but rather “you should not have done it.” He was appealing to an unwavering standard, which he expected you to share, that what you did was wrong.