The decision was based on the court's analysis of English Common Law as it relates to whom a sojourner owes loyalty and obedience. Since the parents were assumed to have been in the United States with the approval of the Sovereign (the United States, itself), then they are assumed to owe loyalty and obedience. Therefore, they are "Subject to the Jurisdiction of". And their son becomes a citizen.
No such description could match an alien in the country illegally. To whom would such an individual owe loyalty and obedience? His native country, clearly, because we have never been allowed to inquire of or vet him, or to constrain him from entering if we determine him an enemy alien.
Here's what Congressman Brian Bilbray had to say:
Our current practice of granting automatic citizenship to anyone born in the United States, including the children of illegal immigrants, is just that -- a practice. The custom has no legal basis. In fact, I believe it is an unintended result of an interpretation of a Supreme Court case involving legal immigrants. To date, the Supreme Court has never ruled on the citizenship of children of illegal immigrants. Accordingly, I think it's time to clarify and resolve this issue once and for all.
Brian is correct. The decision in Wong Kim Ark -- which decided the case of a child of legal entrants -- has been misapplied. No where has a case been tried to adjudicate whether WKA should apply to illegals. Believe me, La Raza, Peter Schey, Gray Davis and Vicente Fox ALL do not want that to happen. It would screw up their plans, since the Supreme Court would slam the door shut.
Read the FAIR article and it's links. Read the WKA decision (it's on line; if you really are honest enough to question your own presuppositions, you can find it). Nowhere has anyone ever said what you said, at least as a court finding. It's just the wishful thinking of those who view invasion of the United States as legitimate.
Here's a little hypothetical for you. Say we have two Al-Qaeda operatives living in Dallas, in the country illegally (I'm sure they're there!). They have a kid, of course paid for by the U.S. taxpayer at Parkland Hospital, home of all illegal aliens. Tell me -- will you and the U.S. government try to convince me that baby terrorist is one of us, due all the rights and privileges of an American?
Just remember, Wong Kim Ark assumes that the parents "owe loyalty and obedience" to the sovereign. The sovereign in the United States is the people and their Constitution. Still think it should apply to these un-nice folks? And if not them, then what makes them different from anyone else in the country illegally?