It is a rueful and cynical Jem and Dill respectively who reflect in the morning upon the events of the trial of Tom Robinson. Having passed Miss Stephanie Crawford and Mr. Avery on the porch as they enter Miss Maudie's house for cake, the children talk with her. She explains to the children that, while Atticus has not won the case, he was able to accomplish something that no one else hitherto has--he kept the jury out longer than in any other case like Tom's.
After they have their cakes, the children go down the steps past Mr. Avery and Miss Crawford who are "still at it." Then, Dill says that he will become a clown when he grows up so that he can laugh at people who talk about others in a disparaging way. "Every one of 'em oughta be ridin' broomsticks. Aunt Rachel already does."
Dill's comment means that the gossips are much like witches. For, they go on the proverbial "witch hunt" to find faults in others that actually reside in themselves. They are unreasonably judgmental and resent anyone who wishes to shake up the conventional wisdom of their setting. This attitude is reflected in Aunt Rachel's earlier comment:
"...if a man like Atticus Finch wants to butt his head against a stone wall it's his head."
Dill is also a victim of the small town's hatefulness. The book implies that people in the town know of his unorthodox home situation and judge him for it. Therefore, he has a personal reason to resent their rumor-mongering.