"Moral relativism" emerged from the realization that no moral truth can be 'proven' to be universally valid. In short, all such truths are beliefs. All beliefs are absolutely valid for their believers and of no consequence to anyone else. For any belief to be imposed on people, for people to be forced against their wills to live in accordance with any belief, is an injustice.

Fortunately, mutual respect as the ethic of justice overcomes all such objections. It contains, as 'the minimum condition of justice', a handful of absolute prohibitions: no killing, harming, coercing, lying, cheating, or stealing to get what you want.