I think I've seen some other comments bring it up, but I'll say it again. I think people who go for the torture are working off a model of linear discomfort addition, in which case the badness of the torture would have to be as bad as 3^^^3 dust particles in the eye to justify taking the dust. However, I'd argue that it's not linear. Two specs of dust is worse than twice as bad as one spec. 3^^^3 people getting specs in their eyes is unimaginably less bad than one person getting 3^^^3 specs (a ridiculous image considering that's throwing universes into a dude's eye). So the spec very well may be less than 1/(3^^^3) as bad as torture.
Even so, I doubt it. So purely utilitarian probably does suggest torture the one guy.
I know I'm way late to the party, but I still gave it a good long think, considering all aspects of the problem before trying to envision a solution. What seems the best solution to me is to return along their own starline, use the several weeks of delay given to evacuate as many people as possible from the connecting colony Huygens (which from the intro is the colony the ship came from through the starline), and then destroy that system, cutting humanity off from the Super Happy Fun aliens, at least for now.
All throughout highschool I wanted to learn to play the guitar. But at that point in time almost everyone I knew was learning to play the guitar, and I sure wasn't going to do what everybody else did. Now, six years later, I'm finally learning. It's a real shame let my disgust of conformity drive me away from putting off something I now love.
A lot of the comments I see seem to be coming from a belief that I am suggesting we throw out or disregard the US Constitution entirely. I'm not. It is mostly a great document for the structure of the country. I'm just suggesting that it shouldn't be taken as the infallible word of demigods. I am guessing most of you don't think of it like that. But I've encountered plenty of people who do.