The trial of Tom Robinson is probably the best example of people speaking freely in To Kill a Mockingbird. Bob Ewell exercises his right to spew his lies and racist hatred while on the witness stand. Although Judge Taylor admonishes him for some of his comments, Bob feels free to say what he thinks, claiming (falsely) that he saw Tom having sexual intercourse with his daughter.
"--I seen that black nigger yonder ruttin' on my Mayella!" (Chapter 17)
Outside the courtroom, Scout and Dill encounter Dolphus Raymond, who they find delights in allowing people to think he is drunken and mentally unstable. He is neither. He is passionate about how badly white people treat Negroes, however.
"Cry about the hell white people give colored folks, without even stopping to think that they're people, too." (Chapter 20)
Atticus' final summation is probably the best example in the novel. He pleads with the jury to put aside their racial bias and judge Tom from the facts presented in the case. Referring to Mayella, and her part in the attack,
"She was white, and she tempted a Negro. She did something that in our society is unspeakable: she kissed a black man. Not an old Uncle, but a strong Negro man. No code mattered to her before she broke it, but it came crashing down on her afterwards." (Chapter 20)