This is more direct, but I always saw the original thought experiment as a way to explore that very concept - is inaction a "choice"? IMO, the only rational answer is Yes.
Even without the third rail, "no choice" is very clearly a choice. People just selfishly want to believe they don't share responsibility if they just let things happen "naturally", as of their inaction means they aren't involved. But they are. We all are. Pretending otherwise is foolish.