At the end of Part 3 I said that I would consider those cases 'when transgression is "cooperative" with, or "competitive" with, a given culture's mores.' I'll stick with the two examples put forth in that essay, but with a preliminary definition of transgressive viewpoint.
My NUM theory of phenomenality is centered almost entirely upon audience-response. For my purposes it doesn't matter whether or not the characters of THE LORD OF THE RINGS think that wizards and dragons are marvelous. All that matters is that the audience reading the book must inevitably think so, since that audience lives in this more phenomenologically uncertain world.
The principle of transgression, however, stems from both the diegetic world of the narrative's characters, as created by the author, and the extra-diegetic world of the audience. For example:
Wilkie Collins' MOONSTONE was published in 1868, and took place within the same time-frame. As I said in Part 3, there's nothing to suggest that either the characters in the novel or the original audience that read the novel regarded first-cousin marriage as transgressive against social mores, at least not when practiced among the aristocracy. Cousin Frank is good and Cousin Godfrey is bad, but the only criterion is only that one is honest and the other is not. In contrast, the 1934 film adaptation of the novel implicitly makes Frank "good" in part because he's entirely unrelated to the heroine, and is hence totally exogamous, unlike Godfrey, who is "bad" in part because he dares to lust after a near relation (though I don't think that the film, unlike the book, specifies how near a relation he is).
So is the cousin-cousin relationship in Collins' original work transgressive at all, if we grant that neither the diegetic characters nor the extra-diegetic audience thought that it transgressed any lawlines?
My verdict is yes, but with the qualification that the MOONSTONE's "incest" is only transgressive-- and clansgressive-- *in posse.* Because a unison of two near relations of roughly the same age strongly *suggests* a unison between blood-siblings, the basic situation of a sexual relationship between cousins will always carry a potential for transgressivity, no matter whether the author makes use of that potential or whether the audience recognizes it.
If Collins' MOONSTONE is clansgressive *in posse,* Mitchell's GONE WITH THE WIND is clansgressive *in esse,* for the 1936 novel is lousy with the symbolic form of brother-sister incest-- which is to say, sexual feelings between brother-in-law and sister-in-law.
I noted in Part 3 that there's no suggestion by Mitchell that she disapproves of the liaison between Ashley and Melanie, and it's not likely that any of her readers did either, as long as it was suggested that the consanguinity was sufficiently distant. Some of Mitchell's readers might not have entirely approved of relations between cousins of any sort in their own time, but Scarlett O'Hara's world had gone with the you-know-what, and so it could be regarded as a charming historical relic whose social rules no longer applied to current practice. This would be in marked contrast to my verdict on the behind-the-scenes tinkering with the 1934 MOONSTONE film. In that work, even though the story still took place in England, the story was also updated to the contemporaneous 1930s-- and so I theorize that the only "cousin-relationship" in the finished film was made to be a marker of evil, in keeping with the screenwriter's anticipation of audience-antipathy for cousin-relationships.
Similarly, there's no sense of opprobrium attached to the romantic intermingling of Ellen and her lost love Phillippe, since by the time the audience learns of it, Phillippe is long dead, and Ellen has married, raised three young daughters, and become a sort of Madonna of the Plantation. Ellen's last word at her death, however, is the name of her lost love, occasioning puzzlement for Scarlett, who unlike the audience never knows anything of her mother's secret romance. However, though the Ellen-Phillippe relationship is not condemned, it also has a quality not found in the Ashley-Melanie relationship: passion. I didn't explain in Part 3 why I considered this relationship "racy" as I called it, but some of the raciness stems from the fact that the Ellen-Phillippe affair is governed by passion, not just a vague inclination between kindred spirits.
The brother-in-law/sister-in-law relationships are characterized by similar passionate spirits. Scarlett, despite her quasi-sisterly relationship to Melanie, tries to get Ashley to run away with her, and he comes damn close to yielding to the Southern vixen. Scarlett doesn't actually care about the two Tarleton Twins that she pulls into her orbit, but they're equally passionate about her, and Mitchell explicitly says that each of them would happy even if the other one married Scarlett-- which suggests almost a "Corsican Brother" level of identification. Finally, there's the convict Archie. This mountain-man character is understandably omitted from the movie, for his only function in the novel is to express scorn for Scarlett when she starts treating white convicts like black slaves at her mill. He's easy to omit from a plot-angle, but he adds a strong humorous element to the postwar section of the novel, not least because he's the only white Southerner who admits outright that he can't stand black people (though of course he does not call them by that name). But he also shows that even with this minor character, Mitchell was fascinated with the brother/sister dynamic, in that Archie's term in prison comes about because he killed his brother for-- what else?-- sleeping with his wife.
All of this should indicate what I've said above: MOONSTONE appears to "cooperate" with societal mores in respect to consanguinity mores, so it keeps its transgressions in the realm of the merely potential. GONE WITH THE WIND finds sneaky ways to flout social mores, and makes those clansgressions seem all the more raunchy for having the allure of the forbidden.