A thought experiment is a lot like a regular experiment, in that you need to isolate the variables being tested if you actually care about answering the question. All of those other factors (i.e. societal implications of torture, the physics which might allow you to inconvenience 3^^^3 people, the effects of mass eye irritation on the annual GDP of Peru) are all irrelevant to the issue; is an incomprehensibly huge amount of harm which is very widely distributed preferable to a large amount of harm inflicted on one person? And, in either case, why?
A thought experiment is a lot like a regular experiment, in that you need to isolate the variables being tested if you actually care about answering the question. All of those other factors (i.e. societal implications of torture, the physics which might allow you to inconvenience 3^^^3 people, the effects of mass eye irritation on the annual GDP of Peru) are all irrelevant to the issue; is an incomprehensibly huge amount of harm which is very widely distributed preferable to a large amount of harm inflicted on one person? And, in either case, why?
In other words, what would your answer be in the Least Convenient Possible World?