[crznp]

Consider this version: there is someone on the track and if I don't act, they will almost certainly die. Or I can act and almost certainly save them, but it sends the trolley somewhere unexpected.

If I were a professional rail operator, I could take action. I know how to operate the switch, I know where both of the lines go, I can contact the trolley operator to let them know what happened. As a bystander, I would not take action. Maybe it would save that person, but dooms all the passengers on the trolley. Maybe someone had it under control and I'm throwing a wrench in their plans. In general, we probably don't want random bystanders to be messing with the operation of heavy machinery.

Sometimes there is a duty to act: if I am babysitting a child and they are suffering in the cold, I better bring them somewhere warm. I may have some responsibility if I see someone suffering in the cold and I have an extra blanket that I could give them. But I am not responsible for buying blankets to give out every time it is cold, nor am I responsible for throwing railroad switches. In those cases, I am more culpable for my actions than my failure to act.