Why does scout's question upset Jem? Is there a simple answer, or any answer, to the question "how can you hate hitler an' then turn around an' be ugly about folks right here at home?"

Jem is most likely worn out from all the talk of the trial. It's obvious that he tries to understand why it came out the way it did. Jem is distressed by the fact that he doesn't understand how men can be unfair to Tom Robinson. Jem is young and he still sees the world as fairly black and white, he's learning there are cruel things that happen and he doesnt want to think about them anymore.

To answer the secoond question. I think people can be blinded by their own faulty actions. It is easy to look at someone else and notice their flaws. It's a much harder thing to recognize those same faults in your own life and act upon them. The truth is it's really sad that the world is like that at all.

I know that all isn't really explained well but i hope you understand the idea of it all.

Some evidence of Jem's frustration about the trial:

"Doesn't make it right," said Jem stolidly. He beat his fist softly on his knee. "You just can't convict a man on evidence like that -- you can't!"