This is a good question. There are many perspectives to consider. On the one hand, Jem has a right to feel disillusioned. His father, Atticus, lost the trial. Therefore, Tom Robinson, an innocent and good man, was charged with a crime that he did not commit, even in the face of overwhelming evidence that he was innocent. Moreover, Tom was shot in prison under suspicious circumstances. Finally, evil touched him as well, as Bob Ewell took matters into his own hands and sought to kill both him and his sister, Scout. Did society get better? The answer is no. From his perspective, Jem could be disillusioned. No one would blame him.
On the other hand, there are good people. Atticus is a hero. Jem knows this. Miss Maudie is a good woman as well. In fact, in a conversation with her, Jem begins to understand that there are other good people in Maycomb. Here is the conversation between Jem and Miss Maudie:
“Who?” Jem’s voice rose. “Who in this town did one thing to help Tom Robinson, just who?"
“His colored friends for one thing, and people like us. People like Judge Taylor. People like Mr. Heck Tate. Stop eating and start thinking, Jem. Did it ever strike you that Judge Taylor naming Atticus to defend that boy was no accident? That Judge Taylor might have had his reasons for naming him?"
This was a thought. Court-appointed defenses were usually given to Maxwell Green, Maycomb’s latest addition to the bar, who needed the experience. Maxwell Green should have had Tom Robinson’s case."
“You think about that,” Miss Maudie was saying. “It was no accident. I was sittin‘ there on the porch last night, waiting.
From this perspective, Jem could be less disillusioned. In my opinion, Jem was less disillusioned. Change takes place slowly, but it does take place.