I’m sympathetic to the following view, which I call moral rationalism:
MR: If S is morally required to do x, then S has decisive reason (all things considered) to do x.
One popular argument for this view appeals to blameworthiness. This sort of argument is found both in Darwall (2006, 287-292) and in Skorupski (1999, 170) as well as in Shafer-Landau (2003, 190-193), although Shafer-Landau employs it to argue for only weak moral rationalism:
WMR: If S is morally required to do x, then S has a (pro tanto) reason to do x.
The following is my reconstruction of their argument.
(1) If S’s doing x is morally wrong, then S would be morally blameworthy for doing x under conditions sufficient for S’s being morally responsible for doing x.
(2) S would be morally blameworthy for doing x under conditions sufficient for S’s being morally responsible for doing x only if S did not have sufficient reason to do x.
Therefore, (3) if S’s doing x is morally wrong, then S does not have sufficient reason to do x. (Those for whom it’s already obvious that (3) is equivalent to MR can stop here.)
(4) S does not have sufficient reason to do x if and only if S has decisive reason not to do x.
Therefore, (5) if S’s doing x is morally wrong, then S has decisive reason not to do x.
(6) S has decisive reason not to do x if and only if S has decisive reason to do ~x.
(7) S’s doing x is morally wrong if and only if S’s doing ~x is morally required.
Therefore, (8) if S’s doing ~x is morally required, then S has decisive reason to do ~x.
(9) We can substitute ‘~x’ for ‘x’ in all of the above without affecting the validity or soundness of the argument.
Therefore, (10) if S’s doing x is morally required, then S has decisive reason to do x.
The premise that does most, if not all, of the heavy lifting here is (2). Here’s why I think that we should endorse (2). One plausible necessary condition for being morally responsible for one’s actions is having control over one’s actions, and one very plausible account of having control over one’s actions is Fischer’s (2006), where one has control over one’s action only if one has the capacity to recognize the relevant reasons and respond appropriately to them. On this view, if one did x, had the capacity to regulate one’s behavior in light of the relevant reasons, and met other epistemic and ownership conditions for moral responsibility, then one was morally responsible for having done x. Now suppose that S has sufficient reason to do x, and in response to the recognition of this fact chooses to do x (this could be because x is the only act alternative that she had sufficient reason to perform or because, of all the act alternatives that she had sufficient reason to perform, she just happened to choose to do x). This means that she is morally responsible for doing x (assuming, of course, that she meets other epistemic and ownership conditions) and thus blameworthy for doing x if x is morally wrong. But how can it be appropriate to hold an agent accountable for doing x on the grounds that she had the capacity to appropriately respond to the relevant reasons, when exercising this very capacity is what leads her to do x (or, at least, it leads her to be rationally ambivalent with respect to a set of alternatives that includes x)? It seems to me that it just doesn’t make sense to hold an agent responsible for doing x because she was, in the given situation, capable of appropriately responding to the relevant reasons and then blame her if she does in fact appropriately respond to the relevant reasons and thereby chooses to do x.
To illustrate, suppose that Jill promised to meet a student, Jack, to review his grade on the last test, but then a once-in-a-lifetime opportunity arises for Jill, and, unfortunately, she must break her promise to Jack in order to take advantage of this opportunity. Assume that the personal benefit for Jane in taking advantage of this opportunity is great enough to give her decisive reason to do so despite the moral reason she has to keep her promise. Now, suppose that Jane, being fully rational and fully informed, recognizes that she has decisive reason to take advantage of this opportunity and as a result chooses to do so, thereby breaking her promise to meet with Jack. What, then, should we say about this case? Possibility A: What she did was all-things-considered wrong, as we all have a prima facie obligation to keep our promises and the fact that she would personally benefit a great deal by breaking her promise is no justification for her doing so. Furthermore, since her act was wrong and since she meets all the conditions for being morally responsible for what she did, she should feel guilt and we should blame her for what she did. Possibility B: Given that she had sufficient (indeed, decisive) reason to break her promise, she was justified in doing so. And thus what she did was not wrong (given MR). Furthermore, she should not feel guilt (and we should not blame her), for it makes sense for her to feel guilt (and for us to blame her) only if she judges (and we judge) that she should regret having done what she did. And although it is certainly appropriate for her to regret having inconvenienced Jack and to regret having to break her promise, she should no more regret having done so than she should have had she been morally obligated to do so, as where, for instance, she had a more stringent moral obligation to take her daughter to the ER instead of keeping her appointment with Jack. Moreover, others should admit that were they in her shoes and fully rational, they too would have broken the promise to Jack. And if others should admit this, then they should not blame her for doing so. In any case, holding her accountable for breaking the promise on the grounds that she was capable of appropriately responding to the relevant reasons and then blaming her for appropriately responding to the reasons by doing what she had decisive reason to do seems entirely unfair and inappropriate.
It seems to me that Possibility B makes a lot more sense. Given the above sorts of considerations, I think we should accept (2) and, consequently, the soundness of the above argument.