The reason I mention this here is because Benhabib's articles set me to thinking about how such theories could be used to describe the process by which chattel slavery became taboo, taboo in the sense that it became something that was completely and permanently off the political agenda. Habermas' stresses the role of interpersonal communication and dialogue in not only coming to agreement on practical measures but also to establish basic norms.
In this passage from "The Utopian Dimension in Communicative Ethics" (New German Critique 35:1985), Benhabib calls attention to the concepts of John Rawls and Jürgen Habermas in developing normative standards through a process of communication by which a rational norm is established:
There are two premises shared by Rawls and Habermas. I will call the first the "consensus principle of legitimacy" and define it as follows: the principle of rational consensus provides the only criterion in light of which the legitimacy of norms and institutional arrangements can be justified. More significantly, Rawls and Habermas share the meta-theoretical premise: the idea of such rational consensus is to be defined procedurally. Rawls maintains that his theory of justice provides us with the only procedure of justification through which valid and binding norms of collective coexistence can be established. Habermas argues that the "ideal speech situation" defines the formal properties of discourses, by engaging in which alone we can attain a rational consensus. The fictive collective choice situation devised by Rawls and the "ideal speech situation" devised by Habermas are normative justification procedures serving to illustrate the consensus principle of legitimacy. [my emphasis in bold]Here I have only some general thoughts about how such a theory might be used to explain the abolition of slavery. Because it clearly didn't happen by a consensus built through rational dialogue.
But values did change. And the new, post-Civil War value that slavery was unacceptable was incorporated into the US Constitution with the 13th Amendment. But it was only the catastrophe of the Civil War that ended the institution itself. The process of the Civil War convinced a big majority of Northerners that slavery really was an abomination that could not be tolerated.
And after the war, the Southern planters accepted that slavery as an institution was gone for good and that advocating its return was a political dead end.
But the norm wasn't established unequivocally. Apologists for the Confederacy to this day continue to defend the antebellum institution of slavery. See: Sean Quinlan and William Ramsey, Southern Slavery As It Wasn’t n/d; Aaron Rupar, Bill O’Reilly: I Wasn’t Defending Slavery, Just Saying Slaves Weren’t Treated So Bad Think Progress 07/27/2016
And there were many lingering effects of slavery and its ideology, from white racist attitudes in general to concrete discrimination against black citizens. Some aspects of the prison system from the end of the Civil War until the present have continued slavery in an explicit way. "Involuntary servitude" in the Thirteen Amendment is specifically allowed for punishment of crimes. And in the postwar South, both the prison system and the sharecropper system continued conditions in which people were confined in a status that was chattel slavery or "involuntary servitude" but wasn't exactly "free labor," either.
I don't have any strong conclusion here about what this says about Habermas' theory of public space and the rational derivation of norms via interactive communication.
But it does seem to me that it's very difficult to separate out the development of the narrative around the shifting norms on slavery from the very contentious political battles, including violent ones and ultimately war, to which the narrative was connected.