This argument reveals a great difference between Jem and Scout. Jem, who is becoming a young adult now, deals with the injustice of the trial by blocking it out and trying to forget about it all. Notice how earlier he was all for becoming a lawyer to try and change things, but at the end of Ch. 26 he is screaming at Scout that he never wants to hear about it again. I think Jem has come to realize that things cannot be changed so easily, which, of course, is all part of growing up and learning that the world is not always a kind and just place.
Scout, on the other hand, is still naive. She cannot understand how Ms. Gates could think Hitler is wrong for the Holocaust when Scout overheard Ms. Gates coming out of the courthouse talking about how it was about time someone taught the blacks in the community a lesson because they might start thinking they were really equal to whites.
Now this confuses Scout because why would Ms Gates feel that way toward blacks yet feel so opposed to Hitler\'s treatment of the Jews. The answer is simple: the color of their skin.
This is an issue Jem has already wrestled with on his own. He cannot resolves how people in their own community can be so hypocritical. So he simply decides to block the memory of the trial from his mind.
Mrs. Gates is Scout's third grade teacher, who discusses current events in class. She taught the students about Hitler and his treatment of the Jews, and proclaimed that he was wrong. Scout realizes that this opinion contradicts Mrs. Gates' opinion of blacks in Maycomb, since Scout heard her say at the trial that they had to be put in "their place, next thing they will think they can marry us." Scout may understand that this is hypocritical in nature, but she does not understand why the contradiction exists. She therefore goes to Jem for advice. When she does, Jem grows angry and tells her that he never wants to hear about the trial again. Jem was profoundly impacted by the outcome of the trial and at this point, he is still trying to sort of his own moral compass.