It doesn't work like that. You need to consider that this is a moral dilemma. You are forced by the circumstances to make difficult moral choices. In fact, you are forced to decide which lives you need to preserve. It’s natural that in these circumstances you will consider the character, achievements and other properties that are morally relevant to decide which lives you will save. It would be ludicrous and arbitrary not to. Your objection that this would lead to a slippery slope in which mass murder would be justified doesn’t work, because the dilemma involves extreme circumstances. Besides, I think that this formulation of the dilemma is excessive because it forces you to push someone and the guy is fat ("fat shaming!"). It is better to consider a scenario in which you can pull a lever to redirect a trolley that will kill five instead of one.
It's a 'leading question' as it were. The greater good is easy to use as an excuse to do whatever you like, and that is exactly how the nazis wound up offing retards and the soviets killing off so many people for wrongthink.
The reality is YOU SIMPLY DO NOT HAVE THE RIGHT to make such decisions. The fat guy's life belongs to him.
And for the dumber people, just look at the possibilities I already listed. What if you kill the guy and it turns out it does no good? That is, you used a rationalization to murder someone and it turned out your rationalization was false. The fat guys doesn't stop the train or else it turns out the train could stop anyway, or the driver switches tracks. Or perhaps the kids set this up intentionally to try to force you to kill that guy.
In real life if you did this retarded action you would go to jail. That is because the law is based on the idea that you don't have the right to decide who lives and dies simply because the outcome would possibly be better for "society" ie you.
This is the basis of marxist philosophy. There is just a big assumption that you can do whatever you choose and a convenient rationalization. Thankfully our laws don't work on such shoddy bullshit thinking, at least not yet, or it would mean the government could just murder whoever they want whenever it's convenient. But go ahead and try and apply it to real life and see how many laws you violate, then ask yourself why.
People's value is not their value to 'society' ie YOU. It is inherent value. If people don't have inherent value then how does society have any value in the first place? Maybe the fat guy is a doctor and the three kids are future murderers, but that is irrelevant or maybe the fat guy is a pedorape and the three kids are future astronauts but that is irrelevant. Either they are human and humans have inherent value ie a soul, or else it doesn't matter whether anyone lives or dies in the first place.This is the same reason a doctor NEVER intentionally harms a patient or denies care. Who the fuck is he to say whether Hitler is a saint or devil? Or whether niggers deserve to have medical care or not? These perceptions change day by day in society but real morality does not change with the direction of the wind.
And that is the real point here, to dehumanize and demoralize students by presenting them a false moral dichotomy. Who is it best to murder? Well, it's worng to murder people, period. And if your philosophy doesn't incorporate that then it is shallow, empty and useless.
If you don't get it from there then there's no helping you.
acOS+Linux. I do find it disrespectful that they say they "read all comments" but didn't respond to the many Mac/Linux users asking for clarification. This from a Windows user. 
