Incidentally, I decided upon consideration of what the math would actually look like for the type of utility function that I'd currently consider reasonable, that given a fixed population, disutility would be basically linear in number of people experiencing dust speck events (the other nonlinearities about one person experiencing a bunch of events would hold though) so am shifting my answer, tenatively, to TORTURE. (Just sticking this comment in this thread since I also made the other claim in this thread.)