Person A: If you become orgasmium, you would feel more pleasure than you otherwise would. Person B: But I don't want to become orgasmium. Person A: But if you want to feel as much pleasure as possible, then you should become orgasmium! Person B: But... I don't want to become orgasmium.

I see Person B's position as being the final word on the matter (especially if, as you say, we're ignoring external consequences). Person A may be entirely right — but so what? Why should that affect Person B's judgments? Why should the mathematical requirements behind Person A's framework have any relevance to Person B's decisions? In other words, why should we be hedonistic utilitarians, if we don't want to be?

The difficulty here, of course, is that Person B is using a cached heuristic that outputs "no" for "become orgasmium"; and we cannot be certain that this heuristic is correct in this case. Just as Person A is using the (almost certainly flawed) heuristic "feel as much pleasure as possible", which outputs "yes" for "become orgasmium".