In addition to the other points I made in this post, I should add that it’s not in fact true that lower-class whites are depicted as the sole source of racism in To Kill a Mockingbird. It’s true that the Ewells are the most egregious example, but really everyone except Atticus Finch “goes along” with racism. Even educated people, such as the Judge, are going along with the racist system, even if they do have some feeling that they ought not to.

That’s sort of a major point of the book, actually, and I’m surprised how many people miss it.