This is a good question and there are two main ironies. First, she is blind. She thinks that she understands democracy, but she does not. More to the point, even a young girl recognizes her inconsistency. For example, in her sanctimonious lesson on the greatness of American democracy, she fails to realize that she and her town are filled with racism and that shortly before they condemned an innocent black man. From this perspective, Maycomb and Nazi Germany are only different by a few degrees.
Then Miss Gates said, “That’s the difference between America and Germany. We are a democracy and Germany is a dictatorship. Dictator-ship,” she said. “Over here we don’t believe in persecuting anybody. Persecution comes from people who are prejudiced. Prejudice,” she enunciated carefully. “There are no better people in the world than the Jews, and why Hitler doesn’t think so is a mystery to me.”
Second and perhaps more seriously Miss Gates is racist. She does not believe that all people are equal. She is incredibly prejudiced and she does not even know it. Scout says to Jem that she overheard Miss Gates talking and what came out was hatred, the ugliest bias, and blind racism.
“Well, coming out of the courthouse that night Miss Gates was—she was goin‘ down the steps in front of us, you musta not seen her—she was talking with Miss Stephanie Crawford. I heard her say it’s time somebody taught ’em a lesson, they were gettin‘ way above themselves, an’ the next thing they think they can do is marry us. Jem, how can you hate Hitler so bad an‘ then turn around and be ugly about folks right at home—”