Perhaps the answer is that there are multiple hierarchies of [dis]utility, for instance: n dust specks (where n is less than enough to permanently damage the eye or equate to a minimal pain unit) is hierarchy 1, a slap in the face is hierarchy 3, torture is hierarchy 50 (these numbers are just an arbitrary example) and the [dis]utility at hierarchy x+1 is infinitely worse than the [dis]utility at hierarchy x. Adding dust specks to more people won't increase the hierarchy, but adding more dust specks to the same person eventually will.