This is either wrong (the utility functions of the people involved aren't queried in the dust speck problem) or so generic as to be encompassed in the concept of "utility calculation".

The utilities of many people are a vector, you are to map it to a scalar value, that loses a lot of information in process, and it seems to me however you do it, leads to some sort of objectionable outcomes. edit: I have a feeling one could define it reasonably with some sort of Kolmogorov complexity like metric that would grow incredibly slowly for the dust specks and would never equate what ever hideously clever thing does our brain do to most of the neurons when we suffer; the suffering beating the dust specks on the complexity (you'd have to write down the largest number you can write down in as many bits as the bits being tortured in the brain; then that number of dust specks starts getting to the torture level). We need to understand how pain works before we can start comparing pain vs dust specks.