I think it would be more concise and accurate to say that the middle class have a vested interest in the permanent existence of a lower class. Racial lines have proven to be a convenient method of separation, because it is easier for white people in the middle class to rationalize the marginalization of “Others” who are visibly different. However, if you are to take history into consideration, the same lines of class division are drawn on a vast number of different pretexts — race, culture, religion, gender.
In fact, any real or imagined difference between people can and will be used as an excuse for more affluent classes to oppress those below them. Racism is deeply ingrained in our culture, but only because it has served the middle class very well as a political tool. If we could wave a magic wand and erase all racist thoughts from the brains of middle-class white people tomorrow morning, we would attach ourselves to some other — equally divisive — philosophy by tomorrow afternoon. We cannot combat insanity on its own terms, and we cannot eliminate racism by drawing battle lines around race.