Atticus is not being sexist when he jokes about women being on the jury. He is just a product of his time and environment.
We should always look at a character’s actions in the context of his society. Although Atticus’s views on women may seem sexist, remember he comes from a very different time and place. In Alabama in the 30’s the social structure was very different. For example, there is the issue of removing women and children from the trial before rape testimony begins. Women need to be protected, like children.
“There has been a request,” Judge Taylor said, “that this courtroom be cleared of spectators, or at least of women and children, a request that will be denied for the time being. People generally see what they look for, and hear what they listen for, and they have the right to subject their children to it.” (chapter 17)
Atticus does not seem to support the argument that women need to be protected. With him, it is all about maintaining the integrity of the jury. We know Atticus’s position on juries from his closing statement.
Gentlemen, 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. (chapter 20)
Indeed, when Jem asks Atticus why there are no women on the jury, Atticus tells him it’s the law and makes a joke about it.
“I do. I guess it’s to protect our frail ladies from sordid cases like Tom’s.
Besides,” Atticus grinned, “I doubt if we’d ever get a complete case tried—the ladies’d be interrupting to ask questions.” (chapter 23)
Atticus explains that people in town don’t like to serve on juries because they don’t want to take sides and offend potential customers.
Serving on a jury forces a man to make up his mind and declare himself about something. Men don’t like to do that. Sometimes it’s unpleasant.” (chapter 23)
Ultimately, it seems that Atticus does not have strong feelings on the subject of women in juries. He just accepts it as the status quo.