If ever you want to refer to an elaboration and justification of this position, see R. M. Hare's two-level utilitarianism, expounded best in this paper: Ethicial Theory and Utilitarianism (see pp. 30-36).

To argue in this way is entirely to neglect the importance for moral philosophy of a study of moral education. Let us suppose that a fully informed archangelic act-utilitarian is thinking about how to bring up his children. He will obviously not bring them up to practise on every occasion on which they are confronted with a moral question the kind of arch angelic thinking that he himself is capable of [complete consequentialist reasoning]; if they are ordinary children, he knows that they will get it wrong. They will not have the time, or the information, or the self-mastery to avoid self-deception prompted by self-interest; this is the real, as opposed to the imagined, veil of ignorance which determines our moral principles.

So he will do two things. First, he will try to implant in them a set of good general principles. I advisedly use the word 'implant'; these are not rules of thumb, but principles which they will not be able to break without the greatest repugnance, and whose breach by others will arouse in them the highest indignation. These will be the principles they will use in their ordinary level-1 moral thinking, especially in situations of stress. Secondly, since he is not always going to be with them, and since they will have to educate their children, and indeed continue to educate themselves, he will teach them,as far as they are able, to do the kind of thinking that he has been doing himself. This thinking will have three functions. First of all, it will be used when the good general principles conflict in particular cases. If the principles have been well chosen, this will happen rarely; but it will happen. Secondly, there will be cases (even rarer) in which, though there is no conflict between general principles, there is something highly unusual about the case which prompts the question whether the general principles are really fitted to deal with it. But thirdly, and much the most important, this level-2 thinking will be used to select the general principles to be taught both to this and to succeeding generations. The general principles may change, and should change (because the environment changes). And note that, if the educator were not (as we have supposed him to be) arch angelic, we could not even assume that the best level-1 principles were imparted in the first place; perhaps they might be improved.

How will the selection be done? By using level-2 thinking to consider cases, both actual and hypothetical, which crucially illustrate, and help to adjudicate, disputes between rival general principles.