When I say, in class or blog, that some thoughts are immoral, there is much resistance. Sometimes, this resistance is formulated as: "Only actions, not thoughts, are immoral." I have argued earlier that voluntary thoughts are actions. In this post, I just want to give a quick argument that some mental activities are immoral.
Suppose Maurice sincerely and prejudicedly believes a racist claim R about members of group G, and he says: "It is my opinion that R." We think Maurice deserves criticism. Even those who think that only physical actions are subject to moral evaluation are likely to agree that something has been done wrong—after all, Maurice has done something physical, namely he has spoken.
But what has gone wrong, and in what way? First of all, it need not be the case that Maurice's speech-act was either morally or rationally criticizable. After all, what he said was true: he said that it was his opinion that R, and indeed it was his opinion that R. He sincerely spoke the truth. What is wrong with that?
We should not criticize Maurice for telling us what his opinion was. We should, instead, criticize him for having that opinion. Now, we have two possibilities here. We can criticize him for epistemic failure, or for both epistemic failure and immorality. If we criticize him for both n the holding of the opinion that R, then we have agreed that mental activities, such as coming to the opinion that R, are subject to immorality.
So, let us explore the option of criticizing Maurice merely epistemically. But if so, then we cannot criticize him any more than we would criticize other people who hold equally or more irrational beliefs, such as that the earth is flat, or that the works of Shakespeare are a 19th century fake, or that the Law of Excluded Middle is false (the last of these is a denial of a law of logic—how much worse can one get than that?). Yet those holding racist beliefs are criticized in a special way, with the criticism not just having to do with the evidential weakness of their views. This suggests that there is something other than mere epistemic failure that is at issue. There is something immoral about coming to racist beliefs in an epistemically deficient way.[note 1]
And in fact I can say a bit about that immorality. We have a special moral obligation—surely not an epistemic one—not to form false beliefs about matters that are socially important, and particularly in cases where having such false beliefs is likely to result in prejudiced unjust behavior. Thus, Maurice should have been particularly careful epistemically in forming the belief R. And this "should have" is a moral "should have".
[Edited: The one time "C" occurred in the original post, it should have been "R".]