Why does widespread agreement on a moral rule not by itself prove that the rule is objectively right?

In the study of ethical relativism, the observation that many societies share certain moral rules does not prove those rules are objectively right because of the logical distinction between facts and values, often referred to as Hume’s Law.12

Even if a moral rule is nearly universal—such as prohibitions against murder or requirements for reciprocity—this commonality is often explained by evolutionary theory or social necessity rather than objective moral truth. Philosophers argue that evolution is a blind force incapable of conferring a moral imprimatur on human behavior. Attempting to derive an "ought" (a moral obligation) from an "is" (a factual observation about human behavior or agreement) is considered a logical fallacy.12

Furthermore, widespread agreement does not preclude the possibility that all participating societies are simply mistaken. If a moral rule were objectively valid, its truth would not depend on the number of people who support it; conversely, if a rule is merely a product of social custom, universal support does not transform that custom into an objective moral fact.1