I would point out here that you're moving the goalposts from your previous argument that "SCOTUS made it up out of thin air!" to "I disagree with SCOTUS' interpretation of the Constitution!"
That SCOTUS made it up out of thin air is not
my previous argument, that would be Doomsought's. To be more particular in my disagreement, the specific quote you gave being the reason is fundamentally at odds with the existence of American Samoa and how recent immigrants are categorized.
The same text is what guarantees immigrants the protection of the law, to my understanding.
Non-citizen residents are a
still existent legal category, on every level of importance to the discussion. So unless you have a ruling saying the free travel guarantee in the Constitution requires a State to
automatically consider any federal citizen in their jurisdiction a state citizen, even while they remain a citizen of a separate state, this makes for a framework that functions perfectly well,
because it's already in use.
Ironically, it is you who are concocting from "thin air" this vague and indeterminate yet somehow compelling interest in people being "right thinking" before they can vote, which exists nowhere in Western philosophy or jurisprudence.
Conflicts of interest are a well established matter in both, and that's what talking of forbidding voting among welfare recipients and holding individuals to having vote-carrying residency in only one state amounts to. Moreso the former, obviously, but with the latter it gives
some shred of pressure to assure the individuals casting votes do in fact think in terms of the good of the state they're voting for representatives in.
The entire reason the emoluments clause exists is because of this concept. While there is a vast difference between overseas noble titles and duel state citizenship of the intra-US sort, the underlying logic for the former being part of the Constitution applies just as well to the latter.
