Joshua Greene has an article in Nature that raises the most interesting question in meta-ethics: what is the relationship between moral psychology and moral philsophy? Unfortunately, the discussion degenerates into a discussion about the least interesting issue in meta-ethics, whether there is a "fact of the matter" about moral judgments.
A few claims (which I may try to justify later):
-The truth that our moral judgments are basically intuitive does not imply anything about their cognitive structure. Our judgments of whether a sentence sounds right are intuitive, but there can still be a science of linguistics inquiring into why we make those judgments.
-Moral psychology can claim to be the proper heir of the Tradition. This is obviously true of Aristotle, Hume and Smith, but it is also true of Kant, Hegel and Mill. The latter all claim that they are theorizing what we instinctively know.
-It is true that a normative conclusion can only be validly drawn from a set of premises if at least one of these premises has a normative element. But this is not that big a deal. It could be that the normative premise is totally uncontroversial or a universal law.
-Anyone who believes that there is at least one act or omission that is impermissible, and accepts the implications of deontic logic (If A is permissible, then not-A is not-obligatory and A is not forbidden, and so on) is as much of a moral realist as anyone needs to be. Such a person is accepting that there are moral truths, just as there are mathematical truths. Further inquiry into the ontological status of moral qualities is about as useful as arguing about the ontology of number. Unfortunately, the former arguments sound relevant to questions like whether Israel has any obligations in war, while the latter don't.
-Normative argument is possible, which seems to me to refute non-cognitivism. It necessarily involves reasoning from premises the interlocutor grants, but neither party to the argument justifies. But it is no different from any other type of argument in that respect.
-Since normative argument relies on the intuitions of interlocutors, it matters what those intuitions are. Therefore, moral psycholgy is relevant to the most normative of moral philosphies.
-Moral psychology holds out the hope of incremental, scientific progress, so it is a better way for academics to spend their professional time.