Throughout the narrative of To Kill a Mockingbird, Atticus Finch displays complete common sense and logic. So, when people go against reason, he is baffled. In Chapter 9, he terms the unreasoning bias of the townspeople "Maycomb's usual disease"; for, when there is "anything involving a Negro," people go "stark raving mad."
Unlike others in Maycomb, Atticus Finch follows a fundamental ethical pattern that does not make exceptions: his belief in the rights of all people under the judicial system of the United States. That is, all people, regardless of color or creed are allowed equal rights under the law. However, the unwritten social code of Maycomb does not adhere to this code, and it is this code that baffles the reasonable Atticus Finch.
In Chapter 20, Atticus professes his belief, as well as declaring that he is no idealist, but simply a believer in the integrity of America's courts. However, the integrity of Maycomb's court is, indeed, compromised.