Similarly, if metaethics is worthy of study, it must be able to say that certain arguments are better than others independently of their likelihood to convince the listener, and why.
Fairly good analogy, but the question you have asked wants an answer. What, in your opinion, makes modus ponens better than appeal to authority, independently of its persuasiveness? I am not sure whether I can formulate it explicitly, and without an explicit formulation it is difficult to apply the idea to ethics.
All my answers to this are flawed. My best is: It's like Euclidean geometry: humans (and other species) are constructed in a way that Euclidean geometry fits fairly well. The formalized rules of Euclidean geometry match spacial reality even better than what we've evolved, so we prefer them... but they're similar enough to what we've evolved that we accept them rather than alternate geometries. Euclidean geometry isn't right - reality is more complex than any system of geometry - but the combination of "works well enough", "improves on our ...
lukeprog gave a list of metaethics questions here:
Most of these questions make no sense to me. I imagine that the moral intuitions in my brain come from a special black box within it, a "morality core" whose outputs I cannot easily change. (Explaining how my "morality core" ended up a certain way is a task for evo psych, not philosophy.) Or I can be more enlightened and adopt Nesov's idea that the "morality core" doesn't exist as a unified device, only as an umbrella name for all the diverse "reasons for action" that my brain can fire. Either perspective can be implemented as a computer program pretty easily, so I don't feel there's any philosophical mystery left over. All we have is factual questions about how people's "morality cores" vary in time and from person to person, how compelling their voices are, finding patterns in their outputs, etc. Can someone explain what problem metaethics is supposed to solve?