Philosophers Philippa Foot and Judith Jarvis Thomson devised a moral thought experiment called the Trolley Problem. It goes like this (in the words of Steven Pinker):

On your morning walk, you see a trolley car hurling 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?

Most people say yes. But consider a slightly different scenario:

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—the same man who was laboring on the spur in the previous scenario. Should you throw the man off the bridge?

Most people say no. The question is why. In both scenarios (1) one person must die to save the five, (2) the fat man is the person who must die if the five are to be saved, and (3) your action is required to save the five. So why is it ok to flip the lever but not toss the fat man? Is it due to the relationship of physical proximity to humanization? That is to say, the closer we are physically to someone, the more we regard their person (similar to the way seeing someone die personalizes the concept of death, much different than mere knowledge that people die). Are we repulsed by the idea of tossing the fat man because his increased physical proximity (actually having to touch the man that is about to die because of our direct action) increases our perception of him as a valuable human being (whereas seeing him from afar and touching a lever does not), raising the emotional stakes too high for us to act as we know we should? If so, then the difference in response is merely emotional, not moral. If you think there is a moral difference between the two, however, what is the moral principle involved?

Now consider another, similar scenario:

On your morning walk you see a trolley car hurling down the track, the conductor slumped over the controls. In the path of the trolley is Osama bin Laden and Mother Theresa. You are standing at a fork in the track and can pull a lever that will divert the trolley onto a spur, saving them both. But doing so would cause the train to run over five murderers. Should one throw the switch (killing the five murderers, and sparing Mother Theresa and bin Laden), or should they do nothing (letting the train kill bin Laden and Mother Theresa?

This one is more complex. Unlike the first and second scenarios, here we have a choice between a group of evil people, and a group consisting of both good and evil people. On the one hand, sparing the most people would require that an innocent person be killed, and evil people live. But we would also kill an extremely evil person in the process. On the other hand, acting to spare one innocent person results not only in the death of five evil people, but also the continued life of a person whose evils add up to more than all the evils of the five murderers combined.

This scenario forces us to think about whether it is permissible to hurt the innocent to punish the evil, and whether the cumulative evil of lesser evil people adds up to more evil than a singular, extremely evil man. What do you think? What would you do?