Ah, but it's not so simple. Here's part of the majority opinion:
"Chinese persons, born out of the United States, remaining subjects of the Emperor of China, and not having become citizens of the United States, are entitled to the protection of, and owe allegiance to, the United States so long as they are permitted by the United States to reside here, and are “subject to the jurisdiction thereof” in the same sense as all other aliens residing in the United States. . . ."
You'll note the "so long as they are permitted by the United States to reside here" part. His parents weren't illegal immigrants. They were 'legally domiciled,' which was a thing at the time. Again, from my understanding it gets more in the weeds than that.
You're confusing the facts of the case with the opinion.
The section you're quoting is a recapitulation of the facts of the case, as agreed upon by all parties. The majority then lays out its legal theory and applies them to the facts, not all of which are relevant to the decision.
The court argues at length that under English Common Law (which is also the law of the United States), anyone born in the country is automatically a citizen, with only two exceptions:
1. Children of accredited diplomats.
2. Children born to hostile foreign armies in belligerent occupation of some part of the country's territory. For example, it cites the case of a child born to the wife of a British soldier during the British occupation of Charleston, during the revolution. That child is not an American citizen.
The court only recognizes one further exception to birthright citizenship:
3. Children born under the jurisdiction of Native American tribes. The court says that the existence of quasi-independent native tribes is a special circumstance with no precedent in English Common Law.
The court specifically argues that English Common Law and the text of the 14th Amendment allow no other exceptions. The concept of "legal domicile" is not relevant to citizenship, and the court specifically states that even the children of sojourners, businesspeople and others only temporarily in the country become citizens at birth. The only exceptions are those I listed above.
The point is that you have to actually read the majority opinion, which argues all of these points at great length.
What Trump is trying to push through, by executive order, would be a massive revision of American law, going back to the Constitution and even before the revolution. The 14th Amendment was intended to make those principles, which Trump is now denying, completely unassailable for all time.
"Chinese persons, born out of the United States, remaining subjects of the Emperor of China, and not having become citizens of the United States, are entitled to the protection of, and owe allegiance to, the United States so long as they are permitted by the United States to reside here, and are “subject to the jurisdiction thereof” in the same sense as all other aliens residing in the United States. . . ."
You'll note the "so long as they are permitted by the United States to reside here" part. His parents weren't illegal immigrants. They were 'legally domiciled,' which was a thing at the time. Again, from my understanding it gets more in the weeds than that.