RE “...He was (at worst) guilty of bad judgment, ...”
I think maybe a little more than just bad judgement, but I understand your point; looking back (a luxury we have), one can make the assertion that IF he had stood up to Hitler, they might averted WWII. As it was, his appeasement actions in 1938 outright doomed millions of Czech citizens to a brutal occupation, and directly led to the decision to invade Polish.
Giving a tyrant what he wants just makes him want more.
Winston Churchill, perhaps because he was a military man himself, knew what was coming, and was repeatedly shouted down until it became apparent what was actually happening. And by then, well... Dunkirk, and the Germans were gazing across the Channel from the shores of France and planning OPeration Sea Lion.
When Hitler ordered the march into the Rhineland in 1936, the French Army alone outnumbered the Germans and the French did nothing. The combined might of France and Britain - right then, at that moment - could have stopped Hitler. But they didn’t.
Again, to your point of WWI - BOTH of those countries paid a horrible price in “The Great War”, and I guess the thinking was “give him what he wants, and he’ll go away”.
A quick study of history, however, shows that’s never the case.
And let’s not forget the fact that France was HAMMERING Germany on war reparations from WWI, which led to the dismal economic conditions in Germany. The Brits even warned the French to notch it down a bit, and they refused.
The stage for the drama of 1939-45, unfortunately, was set at Versaille in 1919... long before the first of Guderians panzers crossed into Poland.
As the stage for WWI was set by the Germans winning the 1870-71 Franco Prussian war, roughly 50 years before that.
Generational animosity...
Therefore, it wasn't unreasonable to assume that Hitler's goal was the unification of German people and that he wouldn't go beyond that. It was only after his pact with Stalin and his seizure of far more than just the Danzig corridor that Hitler became a clear threat to stability in Europe. That simply wasn't the case two years earlier.