what is the irony of Miss Gates lecuture on democracy when compared to her comments at the trial?

Scout's current affairs lesson in school turns into a lesson on Hitler, Jews and anti-Semitism. Scout is curious that although Miss. Gates loathed Hitler and his persecution of Jews, she had said, “it’s time somebody taught them a lesson” about Tom Robinson. Scout wonders why her charity didn't extend to persecuted people in her own community.Atticus gently leads her in this direction and Scout discovers the discrepancy herself.