Hmm... I don't think my point necessarily helps here. I meant that you will always get disutility when you have two desires that always clash (x and not x); whichever way you choose, the other desire won't be fulfilled.

However, in the case you offered (and probably most cases) it's not a good idea to self-modify, as desires don't clash in principle, always. Like with the chocolate and saving kids one, you just have to perform utility calculations to see which way to go (that one is saving kids).