I'm not disagreeing with your sentiment, war is literally hell and the people I know who feel this more strongly are combat veterans, but outright pacifism in the face of a relentless aggressor like the Nazis would have achieved nothing but utter disaster and a "sink into the abyss of a new Dark Age".
Edit: From my own perspective I think our potentially fatal weakness as a species is how easy we are to lead. With a powerful enough leader people will do anything - good or bad.