Utilitarianism is almost certainly much more demanding than Mill allows. It is tempting to think, in fact, that Mill is deliberately being disingenuous here. He was quite aware of how much further there was to go before customary morality became ideal, and that the route to that ideal would seem demanding to many. The rhetoric to encourage people on that road comes in chapter 3 of Utilitarianism, especially in the closing paragraphs. Here, he may be more concerned to allay doubts. Better to persuade a reader to become a feeble utilitarian than put them off entirely by stressing the demandingness of utilitarian morality.
Roger Crisp, Routledge Philosophy Guidebook to Mill on Utilitarianism, London, 1997, p. 115