That is an interesting argument (I've considered it before) though I think it misses the point of the thought experiment. As I understand it, it's not about any of the possible consequences of the dust specks, but about specks as (very minor) intrinsically bad things themselves. It's about whether you're willing to measure the unpleasantness of getting a dust speck in your eye on the same scale as the unpleasantness of being tortured, as (vastly) different in degree rather than fundamentally different in kind.