Well no, miscegenation was nothing I discussed, reread the passage.
But reading it your way still doesn’t allow for the illogic in your reasoning. Miscegenation wasn’t a taboo, it was illegal in this country due to institutionalized racism. Inherent in it was a definition of race that was exclusively phenotypical, ironically many considered partaking in and/or policing of miscegenation were in fact the product of it. Phenotype aside the ever evolving document of our founding stated all men are created equal. Once those considered 3/5 human (even if only .01 of the thing that made them inhuman, bad math for the win) were elevated to human (I see you MLB) then miscegenation was a matter of legality. Marriage has always been between two people. Civilly it’s been a recognized contract between two individuals that conferred certain benefits. As such, changing the definition to add a third person, while not offensive to me, is not the same as recognizing the humanity and following those inalienable rights.
Not only is plural marriage not taboo it’s legal in many countries and cultures, including right here in the USA. That being said, there are zero 14th amendment arguments that can be made for plural marriage