Depends, which one? I'll assume the original. I think I would pull the lever. If I don't pull the lever then I count myself as responsible for the death of those 5 people. If I had the ability to stop it and I willingly turned a blind eye, I think that still counts as responsibility. I would give this answer for every variation unless it was some crazy version like "the 1 guy on track two is the ONLY one with the cure for cancer", but that's just plain silly, forced, and defeats the purpose of the question.