The purported value of ethical relativism, the idea that there are no transcendent, binding rules for right and wrong that all humans are morally required to submit to, is that it allows us to live in peace. That is, if you have your ethics, and I have my ethics, well then there is no real need for us to fight over whose ethic wins. (So long, as, of course, our lives never actually cross.) The real value is far more sinister. We find ethical relativism appealing because we find our own guilt unappealing. Though we seek to suppress such knowledge,...