What does the quote "its just as much Maycomb County as missionary teas" mean?
In Chapter 22, the children return home heartbroken after witnessing racial injustice firsthand at the Tom Robinson trial. Alexandra is waiting at the door for them when they return and asks Atticus if Jem will be alright. Atticus tells his sister that Jem will be fine and says that it was a "little too strong for him." Aunt Alexandra then mentions that she didn't think it was wise to allow the children to go to the trial, and Atticus responds by telling her,
This is their home, sister...We've made it this way for them, they might as well learn to cope with it (Lee 131).
Alexandra then says that the children shouldn't have to go to the courthouse to wallow in it, and Atticus responds by saying,
It's just as much Maycomb County as missionary teas (Lee 132).
Atticus's comment reveals the extent of racial prejudice throughout the small community. Jem and Scout witnessed blatant prejudice at the courthouse, and Atticus believes that the same prejudice is as integral a part of Maycomb as missionary teas. Missionary teas are a significant aspect of Maycomb's culture, and Atticus compares racial prejudice to the well-known community tradition.
Atticus says this to Aunt Alexandra when Jem is so upset after Tom Robinson is declared guilty. Aunt Alexandra thinks the children shouldn't have been allowed to go to the trial, but Atticus justifies it by saying, "This is their home...they might as well learn to cope with it" (Chapter 22). He believes the children should be exposed to the reality of their hometown, the good and the bad. He goes on to emphasize that the injustice of the trial is as much a part of Maycomb as the good parts, as exemplified by things such as missionary teas in Aunt Alexandra's eyes, even though subliminal attitudes of racism are ironically well entrenched there too.
Atticus responds this way when he was chastised for allowing his children to attend the trial. Atticus is making the point that there is as much prejudice at a missionary tea, which people would believe a more appropriate place for children, as there is in the courtroom.