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I think the confusion comes from what you mean by "utilitarian." The whole point of Three Worlds Collide (well, one of the points), is that human preferences are not for happiness alone; the things we value include a life that's not "vapid and devoid of meaning", even if it's happy! That's why (to the extent we have to pick labels) I am a preference utilitarian, which seems to be the most common ethical philosophy I've encountered here (we'll know more when Yvain's survey comes out). If you prefer not to be a Superhappy, then preference utilitarianism says you shouldn't be one.
When you catch yourself saying "the right thing is X, but the world I'd actually want to live in is Y," be careful - a world that's actually optimal would probably be one you want to live in.
I know it's been some time, but I wanted to thank you for the reply. I've thought considerably, and I still feel that I'm right. I'm going to try to explain again.
Sure, we all have our own utility functions. Now, if you're trying to maximize utility for everyone, that's no easy task, and you'll end up with a relatively small amount of utility.
Would you condone someone for forcing someone else to try chocolate, if that person believed it tasted bad, but loved it as soon as they tried it? If someone mentally deranged set themselves on fire and asked you not...