The article is a couple years old, but with the current US presidential election cycle, it seems relevant.
you had Americans meeting Hitler and saying, "This guy is a clown. He's like a caricature of himself." And a lot of them went through this whole litany about how even if Hitler got into a position of power, other German politicians would somehow be able to control him. A lot of German politicians believed this themselves.
If you look back to the very beginning of Hitler's rhetoric about Jews, it was all there -- the talk about extermination and vermin. He didn't spell out exactly what would happen in the Holocaust, but he gave a pretty good indication of its overall thrust. When someone lobs those kinds of rhetorical bombs, it's sort of a natural human tendency to say, "Oh, that's just a figure of speech. They don't really mean it. It's just a way to whip up supporters."