Why does Aunt Alexandra accept that the Cunninghams may be good people, but are not our kind of folks?

In Chapter 23, Atticus tells the children that one person in the Cunningham family was in favor of acquitting Tom Robinson during the jury's deliberation. Jem tells Atticus that he'll never understand those people as long as he lives, and Atticus says that he just has to get to know them. Atticus explains that the Cunninghams have integrity and respect other people. He says they've never taken anything from anybody ever since they migrated from the New World. While Atticus is describing the positive attributes of the Cunningham family, Aunt Alexandra is listening while she "hooks" a rug. Scout mentions that she's going to invite Walter Cunningham Jr. over when school starts. Alexandra says, "We'll see about that" (Lee 299). Scout is surprised and asks why not. Aunt Alexandra says, "Jean Louise, there is no doubt in my mind that they're good folks. But they're not our kind of folks" (Lee 299). Aunt Alexandra tells Scout that the Cunninghams are tacky and dirty. She mentions that they like to fiddle, and have a drinking streak in their family. Scout begins to argue with Alexandra and wants to know why she can't invite Walter over. Alexandra says, "Because---he---is---trash, that's why you can't play with him" (Lee 301). Alexandra is prejudiced towards families who come from a lower social class. She views Walter's family with contempt because she feels they are "beneath" them. Alexandra accepts the fact that the Cunninghams are good folks, but cannot look past their socioeconomic status.