There are two passages that best address this subject in the novel. One can be found in Atticus's memorable summation to the jury. In it he talks about man's prejudices, Tom's innocence, Mayella's tempting of a Negro, the Ewells' contradictory testimony, and the importance of serving on a jury. He lectures the jury to base their verdict on the facts, and not
"... the assumption--the evil assumption--that all Negroes lie, that all Negroes are basically immoral human beings, that all Negro men are not to be trusted around our women..." (Chapter 20)
Atticus concludes by appealing to the jury's sense of honor.
"... a court is no better than each man of you sitting before me on this jury. A court is only as sound as its jury, and a jury is only as sound as the men who make it up... In the name of God, do your duty. (Chapter 20)
Sheriff Heck Tate discusses the evil nature of Bob Ewell before deciding to declare Bob's death self-inflicted. He cannot bring himself to blame Boo Radley for his heroic efforts to save the lives of Jem and Scout.
"There's a black boy dead for no reason, and the man responsible for it's dead. Let the dead bury the dead...
"... To my way of thinkin', Mr. Finch, takin' the one man who's done you and this town a great service an' draggin' him with his shy ways into the limelight--to me, that's a sin. It's a sin and I'm not about to have it on my head. If it was any other man it'd be different. But not this man, Mr. Finch." (Chapter 30)