I think few Americans today have any real understanding of what the world seemed like in the 1930s in Europe.
The Great War was the worst thing to happen there since the Great Plagues. An entire generation of young men was killed or suffered physical or emotional damage that stayed with them for life. The areas in which the actual fighting took place were essentially stripped down to bare earth. Millions of civilians suffered from starvation, and millions more died in the Influenza epidemic of 1918-1919.
They needed everything and for the most part got very little. The Russian Empire crumbled. The Austro-Hungarian Empire crumbled. The Ottoman Empire crumbled. The Balkans balkanized. Governments floundered. Hyperinflation hit Germany and other countries. Then just when things started looking better, a world-wide Depression set in. Even in America, many people thought that capitalism had failed as an ideology.
In America, a leftist government took over. In most of Europe, right-wing forces did. Large percentages of the elites were traditionalist conservatives. They believed in monarchies, in the church, in austerity, and their place in society. Workers had generally been brutalized for generations and so took to communist, socialist, and other leftist movements to try to force power for themselves. The right turned to various shades of fascism in retaliation. This was common throughout western Europe, in Britain, France, Spain, Italy, and some smaller countries.
These fascists didn’t see anything that wrong about Hitler. He was doing everything they wanted their own countries to do. More importantly, he was hating the people they hated: Jews, Communists, liberals, unions. His leadership had made Germany strong while their own governments were weak and ineffectual. The one thing the multiple, ever-changing coalitions running the western countries in the 1930s could agree upon was that war was unthinkable. That meant Hitler also must believe that was was unthinkable.
In hindsight, we know that wasn’t true. But their hindsight told them that the Great War was the worst thing they could imagine and that everything that went into creating that disaster must be avoided.
And America was just as bad if not worse. Our military was pitiful. Our isolationists ruled public opinion. Our fascists drew huge audiences on radio and in person. Our politicians hated spending. Our capitalists were defamed. If America, which didn’t suffer even 1% of what Europe suffered in the war, acted this way, why would you expect other governments to act differently?