You can watch Foucault and Chomsky debate! https://www.youtube.com/watch?v=3wfNl2L0Gf8

Foucault was a degenerate. He espoused a belief in moral relativism to conceal the fact that he was a monster. In reality he was at best a pedophile and at worst a culture destroying sociopath. https://m.youtube.com/watch?v=i63_kAw3WmE

Who arbitrated which is best and which is worst?

According to the moral nihilists and atheists that are Christians, it was God who dictated what is objectively good, bad, ethical, and sociopathic cultural destruction.

So social conservatives are just upset that their authoritative God being is dead. Harsh but true.

That's pure melodrama. There is no God, so he can not die. Good and bad, right and wrong, are usually pretty obvious but people are greedy, weak, and stupid. 16% of the population can't comprehend morality and 50% struggle with the idea. After that it's context, willpower, and virtue. In a game theory sense most people are going to tend towards selfishness and pretend it's self-preservation. It's human behavior.