Noah Millman also comments:

“Throw the switch or not” is a natural choice actually presented by real conditions – switches imply choices by definition. “Push the fat man or don’t” isn’t a natural choice presented by real conditions – it’s a scenario concocted for an experiment. By definition, those cannot be the only options in the universe. And our brains can tell.

It seems to me that what characterizes the people who choose the “logical” answer – push the fat man – is not that they gave a less-emotional response but that they gave a less-inuitive, less-gestalt-based response. They were willing to accept the conditions of the problem as given without question. That’s a response to authority – they are turning off the part of their brains that feels the situation as a real one, and sticking with the part of the brain that reasons from unquestionable givens to undeniable conclusions.

There’s a place for that kind of response – but I would argue that answering questions of great moral import is emphatically not that place. Indeed, from the French Revolution to the Iraq War, modernity is littered with the corpses of those whose deaths were logically necessary for some hypothesized outcome that could not actually have been known with remotely the necessary level of certainty. In that regard, I suspect an aversion to following logic problems to fatal conclusions is not merely a kind of moral appendix handed down from our Stone Age ancestors, but remains positively adaptive.