Trolleys are fun when you take one around Chicago with a bunch of your buddies and binge drink. Trolleys aren't fun when they're runaway-flying down a track towards a fork, on one side of which is trapped one innocent person and on the other side of which are trapped five. You can throw a switch to decide which innocent(s) get(s) splattered. So you choose the one innocent. But what if you have to throw him in front of the trolley to save five others? The response changes here. Most people don't approve of this. And neither do I. The only thing wrong with that is thinking that the two positions are inconsistent. Our moral intuitions are inseparable from our intuitions regarding appropriate and fair norms of social cooperation. If you get stuck in the first trolley travesty, throw the switch! It's the least you can do. We can trust you to make that decision. However, the picture gets much darker in the second trolley travesty, if we start sanctioning the decision making authority of individuals to throw people in front of trolleys. Inevitably, we're going to get some wrong. "Oops, I coulda sworn there were five innocent people stuck on that track and that the only way to save them was to throw Travis in front of the the trolley! How did I know it was just a repair crew and they were gonna move out of the way, or that Travis body would do nothing to slow the trolley?"
These mistakes could just as well happen with the switch throwing, you might argue. I have turned the five innocents into non-innocent repairmen. No fair. Well when I'm standing next to you and we're thinking about the best way to handle the trolley travesty, I don't want to be stuck in the situation of preemptively throwing you in front of a trolley. Herein lies the subtlety I want to introduce. Throwing Travis in front of the trolley may be the right thing to do, just like throwing the switch to kill Travis if he is stuck all alone on the tracks. The thing is, we are averse to this decision because it sanctions vigilantism.
Imagine a crowded street witnessing the trolley travesty take place. 50 people are watching the impending doom of five innocents. Travesty a) they all leap to throw the switch, it is thrown by the closest person, Travis dies, end of story. Travesty b) 25 people turn toward 25 other people, they grab each other, and throw each other in front of the trolley. 50 people die. This does not unfairly alter the scenario, it merely points out the different logical consequences applying subtly different principles.
Keeping the scenario the same, let's say Travis and I are alone to watch the trolley travesty. We both turn to each other and struggle to throw the other in front of the trolley. Perhaps we both die, or perhaps we fail and five people die. Suppose we do the noble thing and we both decide to jump in front of the trolley. We both die. Also, this calls for a lack of regard for ones own life, also an intolerable norm for social cooperation.
To sum this discussion up, to see an inconsistency in taking a different position in travesty 1 than in 2 is to fail to recognize that we subconsciously apply Kantian reasoning:"Act only according to that maxim whereby you can at the same time will that it become a universal law." Nevertheless, this reasoning leads to the wrong decision. Throwing Travis in front of the trolley is the right thing to do, but we don't think in act-utilitarian calculations, we think in terms of social cooperation. More on that distinction later.