Moral Theory and Motivational Contingency

Parfit sometimes suggested that Act Consequentialism might best be understood, not as a moral theory, but as an external rival to morality.  The implicit thought seems to be that morality involves some essentially social mode of thought (perhaps concerned with public codes, or norms of praise and blame, or what principles you'd want everyone to accept), AC does not depend upon any such mode of thought, but it nonetheless offers an account of what you really ought (rather than just "morally ought") to do.

I'm not a fan of that conception of morality, largely because it seems to devalue it, depriving morality of its interest and significance -- if it is not what you really ought to do, then who cares what you "morally ought" to do?  Putting that worry aside, though, it does seem interesting that (only?) consequentialists are apt to regard their normative commitments as not contingent upon being the true moral theory.  That is, if I learned that Kantianism was true, my response (besides incredulity) would be to say, "So much the worse for morality."  In that sense, I don't particularly care about morality, and don't think anyone else should either.  (You should lie to the murderer at the door to save lives, and I don't care about any sense of "wrong" in which doing more good is "wrong".)  But I suspect that, if the roles were reversed, Kantians would not react analogously.  (Can any Kantian readers confirm?)

If that's right, I wonder if anything interesting follows from this observation.  Might it suggest that consequentialism matters more than other theories?  Others seem to depend upon inheriting the normative halo of "morality", whereas consequentialist properties have such clear intrinsic significance that no further halo is required!  Ha, maybe.  More neutrally, it may just be that other theories are so closely tied to some essentially social mode of thought that it's harder to make sense of them mattering without also being what matters morally -- and such a connection needn't have any implications for how much they matter.

A related question (which I owe to David Enoch): how -- if at all -- would (and should) your motivations change upon learning that the meta-normative error theory is correct, and nothing objectively matters at all?  Insofar as you had proper de re desires for what you previously took to be good, it isn't clear why these would be contingent or conditional upon your normative (or meta-normative) beliefs.  Our concern for each individual's welfare, at least, presumably should not be conditional in such a way.  Perhaps deontological concerns -- e.g. to avoid violating rights even if it would overall help people more -- are more appropriately conditional on their actually being right, leaving deontological moral motivation more vulnerable to the threat of moral scepticism?

Another possible exception, even for consequentialists, might involve distant-future non-identity cases (about which it seems difficult to muster direct concern and motivation).  Consider some case where we can either help the already-existing global poor (with no expected downstream effects), or we can bring it about that a whole generation of people a million years hence will be much better off (than the different generation that would otherwise exist in their place).  For purely theoretical reasons, I currently prefer the greater distant good.  But if I came to believe in error theory, I would be much more tempted to just go with my gut, indulge my narrow sympathetic impulses, and help the already-existing people.  (Perhaps a more virtuous consequentialist would have a less theoretically-contingent commitment to the distant future!)

Any thoughts?  Which of your moral motivations do you regard as theoretically contingent in these ways?