It could be argued that the psychological harm imprinted in the minds of those cursed to pull the lever outweigh the outsourcing of killing to other participants. But putting the same burden on everyone? Also who are those tied to the tracks? There is an inherent human incentive to help those one deems close vs people one deems strangers or even enemies. How fast is the train moving? Would it be a slow or swift death? If one person pulls the lever does the game start over? How many levers are there? How many people are there to pull the lever anyway?
If the death toll is n^2 as n approaches infinity with infinite respawing levers, the most physical and psychological harm results from any one of the actors making the decision to pull the levers at any point, and also refraining to pull results in the exact same amount of harm. To have a lever is to kill and die but if there are infinite levers the death continues at the same rate regardless.
Pull it or don't. It doesn't matter.
However if the population increases at a rate faster than the rate the levers respawn, the logical choice is to pull the lever when it comes your turn to reduce suffering, because there is a chance some may never be subjected to the callous games of wretched annihilation.
Cessation of procreation means no more hands cursed to grasp these forsaken levers and no more mangled bodies lying on the tracks.
If the rate the population decreases through antinatalist measures surpasses the rate people die to trains in games, ultimately a trade-off for less suffering results.