Moral of the story is if you don’t completely genocide your enemies, they win.
He turned the whole cast into traitors for no reason. Hate it. Should’ve just ended ambigiously at the rumbling but the author goes out of his way to butcher every character after years of buildup.
Utilitarian moral arguments have no leg to stand on when it comes to survival. The fat man does not have a civil duty to throw himself onto the tracks to stop the proverbial train.