If you believe that today WW2 was "morally clear," what you are saying is that it was clearly worth overcoming all of those risks and that fear (understandable as it is).
They did not do that and instead were spurred into action only when they themselves were attacked, ergo obviously it was not morally clear at the time.
Okay, well I disagree with your dimensional analysis. To me moral clarity is being confident about who is in the right and who is in the wrong. Taking action to do something about it is another matter. To me it's morally clear that Ukraine is in the right in the current war, but I have taken no personal risks to put my life on the line for that belief.
They did not do that and instead were spurred into action only when they themselves were attacked, ergo obviously it was not morally clear at the time.