I agree with you that morality can mostly be framed in terms of volation and an adequate decision theory, but I think you are oversimplifying. For example consider people talking about what other people should want purely for their own good. That might be explainable in terms of projecting their own wants in some way (or perhaps selfish self-delusion), but it doesn't seem like something you could easily predict in advance from reasoning about wants if you were unfamiliar with how people act among each other.