You're given the option to torture everyone in the universe, or inflict a dust speck on everyone in the universe. Either you are the only one in the universe, or there are 3^^^3 perfect copies of you (far enough apart that you will never meet.) In the latter case, all copies of you are chosen, and all make the same choice. (Edit: if they choose specks, each person gets one dust speck. This was not meant to be ambiguous.)
As it happens, a perfect and truthful predictor has declared that you will choose torture iff you are alone.
What do you do?
How does your answer change if the predictor made the copies of you conditional on their prediction?
How does your answer change if, in addition to that, you're told you are the original?
For the case that dust specks aren't additive, assuming we treat copies of me as distinct entities with distinct moral weight, 3^^^3 copies of me is either a net negative - as a result of 3^^^3 lives not worth living - or a net positive - as a result of an additional 3^^^3 lives worth living. The point of the dust speck is that it has only a negligible effect; the weight of the dust speck moral issue is completely subsumed by the weight of the duplicate people issue.
If we don't treat them as distinct moral entities, well, the duplication and the dust speck doesn't enter into it.
I don't think your conceptual problem sufficiently isolates whatever moral quandary you're trying to express; there's just too much going on here.
If you smoke in the smoking lesions scenario, then you shouldn't choose your action here based on how many people would exist, because they would exist anyway. (At least in the first of three cases.)