In reality, the story is quite good at underscoring flaws in the Confederacy.
Scarlett is a bit of a phony and a scamp. She imagines herself a highborn lady of a superior culture, but she will compromise herself to get what she wants. She chases after Ashley Wilkes who symbolizes the plantation society but is also weaker than his symbol. Despite being married to a virtuous lady he draws Scarlett along thereby betraying the nobility he is supposed to represent. In short, the movie shows that Ashley and Scarlett both fail to be what they seem at first, indirectly revealing faults in the foundation of plantation life.
Rhett is a blockade-running rouge. Unlike Ashely and Scarlett he does not pretend to be something else. Since he lives by an independent code, which he will not break, people trust him. Although he is physically drawn to Scarlett he repeatedly mocks her phoniness until their young daughter dies, breaking his last bond to the dishonest Scarlett. Beauty alone was not enough to hold a man who was true to his code.
Meanwhile the story portrays slaves and ex-slaves as compassionate and level-headed. Contrary to criticisms, it undeniably shows them building the foundations of Southern society and its defenses. Yet, in the end Rhett joins the fight to defend it because he is a part of the South. Ultimately, his loyalty is to his own people, despite their flaws. In that sense, they are much like a family.
Much of the movie's message is missed by modern critics because they are unable to detect nuance, a skill they falsely believe to be uniquely theirs. While we can all cringe at moments of black characterization, the movie is generally critical of the South in its original 1939 context. It needs no additional "contextualization" by "experts" who cannot discern anything beyond their narrow field of vision. Finally, nobody should ignore that GWTW actually advanced race relations eighty years ago by awarding the first Academy Award to a black.