Why does Atticus make Scout apologize to Aunt Alexandra?

In chapter 14 of To Kill a Mockingbird, Scout is telling Atticus all about her and Jem's trip to Calpurnia's church while he was away. Atticus seems to enjoy hearing the tale of their adventures, but not Aunt Alexandra; she simply puts down her embroidery and stares. Ever-critical of Atticus's skills as a father, Aunt Alexandra clearly regards the children's visit to Calpurnia's church as another example of Scout and Jem's being allowed to run wild.
Scout then asks Atticus if it's alright for her to go visit Calpurnia's house the following Sunday. Aunt Alexandra immediately jumps straight in:

You may not.

Scout is pretty annoyed at her aunt's unwarranted intervention and lets her know this in no uncertain terms:

I didn’t ask you!

If there's one thing that Atticus simply won't tolerate, it's bad manners. So he immediately tells Scout to apologize to Aunt Alexandra for talking back to her. Scout does as she is told and murmurs an apology. Shortly afterwards, Scout lingers in the hall and listens to Atticus and Aunt Alexandra arguing over—what else?—the best way to raise children. As we saw earlier, Aunt Alexandra is not crazy over Scout going to visit Calpurnia's house, but Atticus is fine with the idea; Calpurnia will look after her there as well as she does at the Finch residence. As well as being critical of her brother's abilities as a father, Alexandra is none too happy with Calpurnia's housekeeping skills and tells Atticus that he should let her go. Atticus, however, has the last word and insists that Calpurnia is going nowhere unless she wants to.