"To Kill A Mockingbird" is one of the most hopeful books of the last century.
When the book begins, Jem and Scout are young and impressionable. They live in a town filled with all kinds of prejudice. The first grade teacher arrived in town with her mind made up. Her rebuke of Scout's ability to read is one example of the book's theme of bias and preconceived ideas. Jem is prejudiced against the confederate widow. The town is prejudiced against the Radley family. Everyone is certain that one man is always drunk. Scout learns later in the book that he is not drunk, he behaves that way as his mechanism for dealing with the prejudice of his neighbors due to his being a white man married to a black woman.
Atticus and his two siblings represent three different approaches to the "small town mentality" in which they grew up. Atticus' brother represents "running away" from the problem and the responsibility. His sister is fully immersed in being Southern. But Atticus is different in that he des not allow the biases of others to control him. He is respectful to all the small minded people whom he meets. His insistence that Jem read to the widow is one of the most important aspects of understanding Atticus' character.
At the end of the book, there are two sets of women. Those in the parlor and those in the kitchen. Scout makes a decision as to what kind of person she will become.
Mockingbirds sing the songs that they hear. (At least that is Harper Lee's viewpoint.) Jem and Scout are in danger of becoming "mockingbirds" at the beginning of the book, but by the end of the book, we can see that like Atticus, they are not going to become "mockingbirds."
The book was published in 1960. It was written, probably, in the late 1950s. At that time, the civil rights movement had not "overcome." The book's view of what Jem and Scout will become is a very hopeful belief that one doesn't have to be a mockingbird in a world of prejudice.
Regrettably, I have loaned my copy of the book out and was not able to verify all the points that I am making, but I hope that you will look at the book again from this perspective.