A runaway trolley will kill five people tied to the tracks. You're on a bridge above them, standing next to a large stranger. Pushing them off would stop the trolley and save the five — they would die on impact. Jumping yourself would not stop it. There is no other option.

Why people split

Those who push reason that consequences are what matter morally: if pulling a lever to redirect a trolley killing one to save five is permissible, then pushing someone off a bridge to achieve the identical outcome must be equally so. The physical mechanism is irrelevant — what is morally relevant is the outcome. Those who refuse invoke the doctrine of double effect and Kantian ethics: in the lever case, the one death is a foreseen but unintended side-effect of diverting the trolley. In the footbridge case, the death is the instrument of rescue — you need the person's body to stop the trolley. Using a human being as a means, not merely as someone who happens to be in the way, crosses a categorical line regardless of the arithmetic.