Trying again here, as I'm not sure I expressed myself well in the previous attempt. The original problem is that you either torture one person or give 3^^^^^3 people dust specks. For purposes of this thought experiment, therefore, we must assume that there exist at least 3^^^^^3 people in some number of universes. So if you asked each and every one of them the formulation I offered in the grandparent, and they all chose the chance of torture based on your reasoning, exactly one of those people would be in for a very unpleasant surprise.

Also, the probability of the torture is greater than the probability of spontaneously converting into a frozen treat for an improbably attractive sasquatch, since we have no reason whatsoever to expect that there is anything that could cause the latter, but we have already taken as a given that there is some individual in the multiverse with the capacity to choose to inflict torture or dust specks.

[Edited] to correct the numbers to be of identical powers.