By not diverting he is choosing to "cause harm." He is no longer able to wish he weren't a part of this. For me, the most interesting part of the question is Further down this line, in another tunnel, only five men are working
further down the line is pretty vague. How far? Far enough to buy time?
We can distinguish between what harm Greg initiates and what harm has already been initiated. Certainly, if Greg could prevent a harm already initiated without initiating harm himself, he should, but the situation presented doesn't allow for that. I don't think that means the five are farther away than the 40. It probably just means everyone but Greg is farther away than the switch.By not diverting he is choosing to "cause harm." He is no longer able to wish he weren't a part of this.
further down the line is pretty vague. How far? Far enough to buy time?