Which is a real-world morality argument that has been raging, off an on, for probably about two centuries or better now. There are people in the real world who very much believe in that stance as part of their backing of moral relativism.
Well, whoever is doing that is being silly. For this argument, are we agreed that in order to qualify as "Chaotic X" rather than "Neutral X," the person being referred to must have a deep and thoroughgoing commitment to the principles associated with "being Chaotic"? If so, then what you're saying is that a really hardcore moral relativist is first saying, "all moral value judgments only make sense relative to a specific culture," and then turning around and saying, "relativism is morally superior to absolutism." Those two things are incompatible--because the latter is a statement made about moral values,
sans cultural context--true for ALL cultural systems. But...that's exactly the kind of moral statement the hardcore relativist cannot accept! It makes a moral value judgment that applies across all cultures, social groupings, etc. In other words, it is a
moral absolute, which hardcore relativism cannot abide.
Now, if they were to make a much weaker and more narrow argument, e.g. "within culture X, relativism leads to better results than absolutism" (weakened both because it specifies a single culture, and because it makes an empirical rather than philosophical standard), that would be a very different story...but that's not at all how the Law/Chaos dichotomy is presented in literature, D&D or otherwise. Instead, it's very clearly presented as the "hardcore" Chaotic people thinking that their system is universally better--better for all people in all places and times--than Law, and vice-versa. Such a two-way "sneering" contest flat out isn't possible if one side is ardently committed to the idea that moral value ONLY has significance when constructed within one specific cultural group among many (potential*) groups.
*It's important to note here that at least the
potential for other cultural groups is necessary for an ethical theory to remain "relativist." If an ethical theory posits that in truth there is really only one gigantic culture, shared by all of its individual members and merely giving the
appearance of subdivision, it's no longer relativist--it's
subjectivist, which is an entirely different beast.