Liz Harman's excellent Madison Metaethics talk on 'The Irrelevance of Moral Uncertainty' [pdf]* got me thinking again about whether false normative beliefs can be justified. As I previously noted, we might think that the fundamental normative truths, being non-contingent and presumably a priori, are always what it'd be ideally rational to believe. Then again, insofar as they can also be highly non-obvious, we might think there's an important (less "strict") sense in which we rationally ought to apportion our credences broadly over a range of competing normative views.
One reason you might think that false moral beliefs can be justified is that we can have "procedural" (e.g. testimonial) evidence for any claim whatsoever. For example, if everyone a mafioso trusts and respects since childhood has drummed into them that it's right to kill innocent people to promote the family's financial interests, perhaps you'll allow that there's some sense in which they end up being "justified" or "reasonable" in believing this.
Nonetheless (as Liz argued), this doesn't seem to justify their immoral actions in any significant sense -- the mafioso is still blameworthy when they kill innocent people, since they are in fact showing insufficient regard for others' interests, no matter how laudable they believe themselves to be. So this kind of case -- involving what I've called "procedural" kinds of evidence -- seems problematic for Uncertaintism: the view that what we ought to do depends on our moral credences (as well as our ordinary credences about non-moral matters of fact). As this case shows, false moral views supported on merely "procedural" grounds seem not to influence what we ought to do.
However, I think it would be too quick to conclude on these grounds that uncertaintism is false. For that would be to neglect that, "procedural" evidence aside, one might also think we can have "substantive" reasons to believe certain false normative views -- reasons to believe them simply in virtue of the intrinsic credibility of their content. Not beliefs like the mafioso's, presumably (they seem intrinsically morally repugnant). But the kinds of moral views that philosophers reasonably dispute. To borrow an example suggested by Jamie Dreier in the Q&A: Suppose you can either prevent one death or one million headaches (supposing that the latter is just slightly greater in terms of aggregate utility). Suppose utilitarians are actually right in claiming that you should prevent the headaches in this sort of case (though it's a close call), and that the competing anti-aggregative view (i) is intrinsically credible, at least to some non-trivial extent; and (ii) holds that it would be much worse, morally speaking, to prevent the headaches. In such a case, the "uncertaintist" claim -- that you should "play it safe" by preventing the one death -- seems more plausible.
Now, I'm not sure whether uncertaintism is right even about this case. Perhaps no false a priori claims can be "intrinsically credible" in the required sense -- perhaps any candidates we might put forward are merely psychologically "credible"-seeming to us, and not really intrinsically credible (or warranting credence simply in virtue of their content) in the way that true a priori claims presumably are. To think otherwise would certainly raise puzzling questions about how (some but not other) false contents could be intrinsically credible in this way.
But it seems to me that the best hopes for uncertaintism rest on this question. If some false moral views are intrinsically credible in this way, then it's plausible that we really ought to take these "moral risks" into account. But if false moral views are never intrinsically credible -- so that any possible "justification" for them takes the merely procedural form found in the Mafioso case -- then Liz's case against uncertaintism seems to me very persuasive.
* [Update: PDF shared with permission]