Steven Pinker in the New York Times Magazine:

The gap between people’s convictions and their justifications is also on display in the favorite new sandbox for moral psychologists, a thought experiment devised by the philosophers Philippa Foot and Judith Jarvis Thomson called the Trolley Problem. On your morning walk, you see a trolley car hurtling down the track, the conductor slumped over the controls. In the path of the trolley are five men working on the track, oblivious to the danger. You are standing at a fork in the track and can pull a lever that will divert the trolley onto a spur, saving the five men. Unfortunately, the trolley would then run over a single worker who is laboring on the spur. Is it permissible to throw the switch, killing one man to save five? Almost everyone says “yes.”
Consider now a different scene. You are on a bridge overlooking the tracks and have spotted the runaway trolley bearing down on the five workers. Now the only way to stop the trolley is to throw a heavy object in its path. And the only heavy object within reach is a fat man standing next to you. Should you throw the man off the bridge? Both dilemmas present you with the option of sacrificing one life to save five, and so, by the utilitarian standard of what would result in the greatest good for the greatest number, the two dilemmas are morally equivalent. But most people don’t see it that way: though they would pull the switch in the first dilemma, they would not heave the fat man in the second. When pressed for a reason, they can’t come up with anything coherent, though moral philosophers haven’t had an easy time coming up with a relevant difference, either.

I’m a little surprised at the comment about moral philosophers. It would of course be impossible to come up with a distinction that justifies the different responses and would satisfy all moral philosophers. But it doesn’t seem so hard to come up with something “coherent” in the everyday sense of that word. In the switch-the-track case, you’re not causing anyone’s death as a means to the end of saving other lives. In the fat-man case, you are. I understand that there are moral philosophies that deny the importance of this type of distinction, but there doesn’t seem to be anything incoherent about it.