The issue with a utility function U(T,S) = ST + S is that there is no motivation to have torture's utility depend on dust's utility. They are distinct and independent events, and in no way will additional specks worsen torture. If it is posited that dust specks asymptotically approach a bound lower than torture's bound, order issues present themselves and there should be rational preferences that place certain evils at such order that people should be unable to do anything but act to prevent those evils.
There's additional problems here, like the idea that ...
A dust speck in the eye with no external ill effects was chosen as the largest non-zero negative utility. Torture, absent external effects (e.g., suicide), for any finite time, is a finite amount of negative utility. Death in a world of literal immortality cuts off an infinite amount of utility. There is a break in the continuum here.
If you don't accept that dust specks are negative utility, you didn't follow the rules. Pick a new tiny ill effect (like a stubbed toe) and rethink the problem.
If you still don't like it because for a given utility n, n + n !=...
Maybe I'm mistaken, but I think this is a pretty good example of how easily people get hung up on a false dichotomy.
If you don't accept the additivity of harm, you accept that for any harm x, there is some number of people y where 2^y people suffering x harm is the same welfare wise as y people suffering x harm.
(Not to mention that when normalized across people, utils are meant to provide direct and simple mathematical comparisons. In this case, it doesn't really matter how the normalization occurs as the inequality stands for any epsilon of dust-speck harm greater than zero.)
Polling people to find if they will take a dust speck grants an external harm to the torture (e... (read more)