The phrase “moral relativism” is usually considered a scornful term today. It is often used to discredit an opponent’s moral position by those who more or less subscribe to the idea that universal and objective moral truths exist, that all humans can discover them, and that morality, like science, can be progressive (less often the term is misapplied to suggest a plainly dishonest or inconsistent moral position). In this essay, Jesse Prinz attempts to dignify the phrase by arguing that moral relativism is in fact true.

Suppose you have a moral disagreement with someone, for example, a disagreement about whether it is okay to live in a society where the amount of money you are born with is the primary determinant of how wealthy you will end up. In pursuing this debate, you assume that you are correct about the issue and that your conversation partner is mistaken. Your conversation partner assumes that you are making the blunder. In other words, you both assume that only one of you can be correct. Relativists reject this assumption. They believe that conflicting moral beliefs can both be true. The staunch socialist and righteous royalist are equally right; they just occupy different moral worldviews.

Relativism has been widely criticized. It is attacked as being sophomoric, pernicious, and even incoherent. Moral philosophers, theologians, and social scientists try to identify objective values so as to forestall the relativist menace. I think these efforts have failed. Moral relativism is a plausible doctrine, and it has important implications for how we conduct our lives, organize our societies, and deal with others.

More here (PDF).