There was some discussion of this on the Missouri philosophy blog a while back. I suggested that actions are "permissible by default", and that constructing a positive argument for the permissibility of homosexual acts is as superfluous as arguing for the permissibility of eating icecream. The onus is on the moral scold. Andrew Moon responded that we may be justified in believing something to be wrong even if we can't immediately produce an argument to support this belief. I clarified my point as follows:
Andrew - I meant the ‘permissible by default’ thesis to be fundamentally metaphysical in nature. That is, an act is permissible unless there is in fact some reason why it’s wrong.
The methodological implication is that we shouldn’t expect any explanation to be given of why permissible acts are permissible (except for the trite “it harms no-one”, etc. — cf. the ice cream case). If we are to engage the moral question philosophically, the only way to do this is to see if there are any arguments for impermissibility that stand up to scrutiny.
As an epistemic point, of course, people don’t always need to do moral philosophy before having justified moral beliefs. But it’s also obviously true that your mere intuition isn’t enough — just look at all the past bigots to whom it “seemed” that interracial marriage was wrong. I’d guess the epistemic question must be settled by factors external to the immediate phenomenology, e.g. whether your moral intuitions are actually reliable, or something along those lines.
That still doesn’t speak to the practical point, of what subjective guidance one can give an agent here. How about this: if it seems to you that X is wrong, then you may tentatively suppose this to be so, BUT if other epistemically responsible agents call this into question, you ought to put aside your mere intuition and see whether there is any actual reason that can ground it. (If, at the end of inquiry, you can find no good arguments for the impermissibility of X, this would seem pretty strong evidence that in fact you are in the same position as the racists of yesterday.)
Unfortunately, no-one ever responded to these suggestions, so I reproduce them here instead. Any thoughts?