But the problem is that it is needlessly complicated, and the complications are what make the decisionmaking difficult. If the question was "You must flip a switch to the left or to the right. If you flip it to the right, one person will die. If you flip it to the left, five people will die. Again, you must flip the switch. Which way do you flip it?" everybody would give the same answer.

Instead, of "you must flip the switch" you get a speeding train. Instead of the switch you get fat people and bridges. Are the five people children and does the fat person have heart trouble? Is the fat person fat because he's greedy, or does he have a glandular problem. Will anyone see me pushing the fat man? And again, what guarantee do I have that a fat man's body will stop a train? How old is the fat man? How young are the kids? Are there suspicious looking people around who, if the train fails to run over the five people, will just back the train up and try again?