To continue this business of looking at the problem from different angles:

Another formulation, complementary to Andrew Macdonald's, would be: Should 3^^^3 people each volunteer to experience a speck in the eye, in order to save one person from fifty years of torture?

And with respect to utility functions: Another nonlinear way to aggregate individual disutilities x, y, z... is just to take the maximum, and to say that a situation is only as bad as the worst thing happening to any individual in that situation. This could be defended if one's assignment of utilities was based on intensity of experience, for example. There is no-one actually having a bad experience with 3^^^3 times the badness of a speck in the eye. As for the fact that two people suffering identically turns out to be no worse than just one - accepting a few counterintuitive conclusions is a small price to pay for simplicity, right?