An interesting related question would be: What would people in a big population Q choose if given alternatives: extreme pain with probability p=1/Q or tiny pain with probability p=1. In the framework of expected utility theory you'd have to include not only the sizes of the pains and size of populations but also the risk aversion of the person asked. So its not only about adding up small utilities.
Today's post, Torture vs. Dust Specks was originally published on 30 October 2007. A summary (taken from the LW wiki):
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