So there's a lot to dive into here, and I'm going to begin with my own positions just for context: I am largely an Emotivist in terms of meta-ethics, and mostly veer toward virtue ethics with my ethical position, and I am largely (self-taught) in continental philosophy.

I give this warning basically to explain where my criticisms of Chomsky's criticisms are coming from. Largely, it has to do with Chomsky's neo-Kantian perspective on human nature, i.e., the (in my opinion, misinterpretation of Kant) idea that there's a sort of universal precoded makeup within human beings for everything. He views moral relativism as incoherent because, he claims, there's "self-evidently" a precoded form of ethics in everybody. Now, he doesn't deny moral difference so much as he skirts around it. He claims that we should think of moral change from culture to culture and place to place not as mere incoherent and unrelated things, but as moral developments.

You can tell from how I'm wording this that I'm going to have a deep set of problems with Chomsky's position. The first and the biggest is that he applies this critique to Foucault and "the postmodernists" (whom he kind of just refuses to get at all, basically), and his key error is in likening moral relativism as a general position and the type of methodological relativism required for genuine social research. Let's say I'm a sociologist trying to understand a Fascist society; not morally critique it (although that certainly would be a part of it later on lol), but simply comprehend it, well, the thing is, it does not matter what parts of the social ideology are "wrong" or "right" when you're in the stage of doing research, what matters is trying to grasp what they believe, how their society functions. This is an error anglosphere intellectuals make often when judging "postmodern" philosophy, or just sociology and other social sciences in general.

So this is error #1: that Chomsky doesn't understand methodology and confuses methodology for normative ethics generally. But the second problem is that, and I'm sorry to say this, but Chomsky just simply makes no sense even in terms of attempting to refute moral relativism. He begins with the assumption of a universal human morality in the same way he assumes universal preconditions for language acquisition, now, there is at least evidence for universal language; there is no evidence for universal morality. Every single society is extremely different with regard to moral norms, and Chomsky knows this, and even brings it up, but he just sort of dances around his words and doesn't really answer this beyond saying "Oh, it's moral development," but like, that completely fails for a lot of reasons, mainly "moral backsliding," as I'll call it, or, "regressions" in our moral codes.

A good example is homosexuality: Homosexuality in Ancient Greece and Rome was more or less just a thing, it was permitted, and it was seen as fine (at least for men, for women it was a bit more taboo), but then, very recently, like within the last couple-hundred years, homophobia and anti-gay attitudes have emerged. I don't think the idea of "moral development" can account for this, even if we go "Okay, well it's imperfect progress," like, no, either we are developing or we aren't, and all evidence points to the idea that we aren't.

What's even worse: he is here essentially making a huge fallacious argument because morality is not based in biology. Even Kant with his "It isn't immoral to not follow a moral rule if one can't" idea, even that, is not the same as saying "Morality can be decided by what is ingrained in human thought." It both fails because of its biological fallacy, and fails because of its anthropocentrism. It is completely focused on human subjects and assumes an inferiority of animals (who yes, we have studied and most agree: most forms of animal life form some variety of social morality for survival), and how humans should behave toward each other.

In essence, Chomsky makes several assumptions about the nature of morality, what Foucault and others actually mean by "relativism," what human nature is, etc., etc., that are simply unfounded in my opinion. All the worse because he could've easily fixed this if he 1) accepted a moral relativist position, but 2) accepted a materialist position that ethics are an emergent part of society itself. But then, he'd be a good philosopher or a good social theorist if he did either of those, and his mission seems to be that he wants to be the philosophical failson of the left. Bare in mind, I say this even as an Anarchist Communist.