The history of SCOTUS in the 20th Century and beyond has been sweeping overrule of long-standing precedent, here and in other areas also, without any constitutional explanation, reasoning, or justification. The results have aided greatly in the catastrophic increase of unconstitutional power of the federal government.
You are relatively new here, so you missed the earliest discussion of the Slaughterhouse Cases here on FR out of which the article I linked (that from what I can tell you didn't read) grew.
Miller's thesis to interpret the entire amendment was not directly germane to the case, and therefore dicta. Moreover, the citizenship clause as excluding corporations was actually contrary to the intent of the authors of that clause (Bingham and Conkling) although it was likely not even considered by many of the legislatures that ratified it. I may disagree with the citizenship clause and its fraudulent intent, but its secret intent was clearly to include fictitious persons as deserving equal protection. Miller's interpretation was a stop-gap move. When it was later weakend in Gitlow v. New York (which applied only to the First Amendment and was therefore the beginning of selective incorporation) and finally bypassed by John Chandler Bancroft Davis' completely bogus headnote in Santa Clara County v. Southern Pacific Railroad, SCOTUS' performance went from bad to worse.
Nevertheless, "selective incorporation" is the law of the land today, bogus or not, like it or not.