This is actually a really interesting one! It questions your faith in humanity. All everyone has to do is not pull the lever. If the remaining population of humanity is on the 33rd switch, then just 33 randomly selected people all have to not choose to kill anyone. But can you trust such a huge decision to a stranger? Will the person further down the tract trust them or kill more people to safeguard humanity?
Personally, I think one life is worth sparing humanity this risk of annihilation. I could live in a world where my life might be randomly sacrificed to safeguard humanity if it only happens once.