By being there you're already involved whether you want to be or not. You're in it now and you're expected to make a choice. Failure to choose is also one of the choices.

The lever operator can't be at fault, or to blame, for the situation - but they are absolutely involved. That's the point of the exercise. From the moment you notice the trolley tracks and the lever you are now entwined with the fates of the people that are here, and the trolley problem will force you to choose a bad solution that you won't feel good about - because there are no good solutions. It's the Kobayashi Maru of psychological exercises.