This is hardly what the American founders envisioned for a free society. The sheer diversity of moral and religious ideas within and between societies is invoked as evidence for relativism. We are left with relativism. Here again, the facts do not deliver the conclusion. A diversity of ethical and religious beliefs hardly insures that they are all somehow true.
Ethical relativism eliminates the notion of a moral mistake.
But this is just as fallacious as saying that every answer on a multiple-choice test is correct because there is a diversity of answers. There may also be less diversity between cultures than is often thought. Every culture has taboos against stealing. Yet a desert culture may penalize the theft of water much more highly than would a tropical culture. As Paul tells us in Romans 1-2, God has endowed with a conscience all those created in His own image, however much we efface or neglect it.