You notice that the brakes of a nearby trolley have suddenly failed. There are five people on the track ahead of the trolley. There is no way that they can get off the track before the trolley hits them. There is a lever near you that you can pull which diverts the trolley to a secondary path. Unfortunately there is one person lying on the secondary path who has no way of moving in time before the trolley gets to him if you pull the lever. You can turn the trolley, killing one person; or you can allow the trolley to continue on its current path, killing five people.

Is it more moral to pull the lever or not?

This thought experiment comes with the following variant:

You are on a footbridge above the train tracks. You can see that the trolley approaching the bridge is out of control, and that it is going to hit five people who are stuck on the track just past the bridge. The only way to stop the train is to drop a heavy weight into its path. The only available heavy enough weight is a very fat man, who is also watching the train from the footbridge. You can push the fat man onto the track into the path of the train, which will kill him but save the five people already on the track; or you can allow the train to continue on its way, which will mean that the five will die.

Do you push the fat guy or not? And how is this different than the previous scenario?

Another small variant:

Okay so this scenario is identical to the preceding scenario but with one crucial difference. This time you know with absolute certainty that the fat man on the bridge is responsible for the failure of the trolley's brakes: upset by fare increases, he sabotaged the brakes with the intention of causing an accident. As before, the only way to stop the trolley and save the lives of the five people already on the track is to push the fat saboteur off the bridge into the path of the train.

Does fatty saboteur get a shove?

And the last one, a different but related scenario:

A brilliant transplant surgeon has five patients, each in need of a different organ, each of whom will die without that organ. Unfortunately, there are no organs available to perform any of these five transplant operations. A healthy young traveler, just passing through the city the doctor works in, comes in for a routine checkup. In the course of doing the checkup, the doctor discovers that his organs are compatible with all five of his dying patients. Suppose further that if the young man were to disappear, no one would suspect the doctor.

What is the moral thing to do.

If your moral response is different in these (especially the first two) scenarios, what is it that is different about the scenarios that warrants a different response?