The Idlers' Club is a group of old men who spend time near the courthouse discussing the most prominent town news and issues. The group is cast in a negative light, because its members are idle, that is, they like to gossip and waste their time talking about anything because they have nothing more important to do:
This was a group of white-shirted, khaki-trousered, suspendered old men who had spent their lives doing nothing and passed their twilight days doing same on pine benches under the live oaks on the square.
When Scout and Jem's father, Atticus, decides to defend Tom Robinson, a black man who is falsely accused of raping a local white woman, Mayella Ewell, Atticus is criticized by the town people and becomes the main center of gossip. This is because locals cannot comprehend the fact that a prominent attorney would agree to defend a black man accused of raping a white woman. In Alabama at that time, racism was rampant and black people were undervalued and looked down upon.
So, Jem and Scout become the victims of the situation and, willing to discover more information about the affair, they frequent the courthouse and find the most reliable information from the Idlers' Club members. The group does not like the idea of a black man being defended and while one says that "the court appointed [Atticus] to defend this nigger," another member dismisses the idea and complains that Atticus really wants to defend Tom Robinson to the best of his ability, even if it entails degrading the local white people who accused Tom--Bob and Mayella Ewell:
"Yeah, but Atticus aims to defend him. That’s what I don’t like about it."
All of this confuses Scout, and she wonders why her father did not tell her that he was appointed to defend Tom.
The group's discussion reveals how prejudiced and hostile its members are towards the blacks, and this produces a sense of condemnation among the readers. People like the members of the Idlers' Club embody the malice which threatens to destroy all that is innocent, like Tom Robinson, one of the novel's "mockingbirds" (a mockingbird is a symbol for something that is innocent and uncorrupted).