Sally Adee in The Last Word on Nothing:
Stop me if you’ve heard this one. A trolley carrying five school children is headed for a cliff. You happen to be standing at the switch, and you could save their lives by diverting the trolley to another track. But there he is – an innocent fat man, picking daisies on that second track, oblivious to the rolling thunder (potentially) hurtling his way. Divert the trolley, and you save the kids and kill a person. Do nothing, and you have killed no one but five children are dead. Which is the greater moral good?
This kind of thought experiment is known as a sacrificial dilemma, and it’s useful for teaching college freshmen about moral philosophy. What you maybe shouldn’t do is ask a guy on the street to answer these questions in an fMRI machine, and then use his answers to draw grand conclusions about the neurophysiological correlates of moral reasoning. But that’s exactly what some neuroscientists are doing. The trouble is, their growing body of research is built on a philosophical house of cards: sacrificial dilemmas are turning out to be exactly the opposite of what we thought they were. Guy Kahane wants to divert this trolley before it drives off a cliff.
Kahane, deputy director of Oxford’s Uehiro Centre for Practical Ethics, has never been a big fan of the sacrificial dilemma. The main problem, he says, is that it has been misapplied to situations it was never intended for.