How we cite our quotes: (Chapter.Paragraph)
Quote #1
Mammy was black, but her code of conduct and her sense of pride were as high as or higher than those of her owners. (2.5)
Many of the black characters in the novel are obsessed with social class, and see their status linked to that of their owners. Having the people on the bottom of the social scale enthusiastically endorse the status quo is supposed to make the status quo look okay; if the folks on the bottom are happy, what's the problem? It also makes it appear that Mammy is part of the family, connected to Scarlett by love rather than because her labor and her life have been taken from her by force.
This might be a good moment to mention that in Alice Randall's The Wind Done Gone, a parody/sequel/critique of Gone With the Wind, Gerald sleeps with Mammy, and has a daughter by her. Relations between masters and slaves, often involving outright rape or some form of coercion, were fairly common. Even being literally part of the family (half-sisters and half-brothers) didn't change the class status of black people in the old South—and in fact could just serve to emphasize it in particularly painful ways.
Quote #2
[…] she respected them, and, in time, learned to admire the frankness and forthrightness of these people, who had few reticences and who valued a man for what he was. (3.98)
Ellen admires her neighbors at Tara for not being as class-conscious as her own family. The idea that they "valued a man for what he was" is ludicrous, though. The first thing Ellen's neighbors see is not whether a man has value, but whether he's white or black. This line is a lie—and, in this vein, the whole novel could be seen as one long, vicious lie about social class.
Quote #3
Of course he wasn't a gentleman and there was no telling what men would do when they weren't gentlemen. There was no standard to judge them by. (9.139)
Rhett isn't a gentleman since he refuses to abide by the rules of class. This makes him dangerous and disturbing; the novel as a whole doesn't like war and revolution and people getting out of place. Or does it? The old South, where women couldn't even eat for fear of looking un-dainty, also comes across in the book as restrictive and stultifying. From that perspective, Rhett's freedom from class makes him exciting and sexy. He can do anything.