Personally, on reading the story, I decided immediately that not only would I not walk away from Omelas (which solves nothing anyway,) I was fully in favor of the building of Omelases, provided that even more efficient methods of producing prosperity were not forthcoming.

The prevention of dust specks may vanish into nothing in my intuitive utility calculations, but it immediately hits me that a single tortured child is peanuts besides the cumulative mass of suffering that goes on in our world all the time. With a hundred thousand dollars or so to the right charity, you could probably prevent a lot more disutility than that of the tortured child. If for that money I could either save one child from that fate, or create a city like Omelas minus the sacrifice, then it seems obvious to me that creating the city is a better bargain.