It is not a truism if there are people within the United States who are not subject to its jurisdiction.
Even then, that is not the test. The test is: "who is subject to the jurisdiction of the United States"?
It was this that I replied to: "Any person within our borders is subject to the jurisdiction of the United States (for the most part, diplomatic immunity aside)"
The clause, "who is subject to the jurisdiction of the United States" is a truism if "any person within our borders is subject to the jurisdiction of the United States".
I'm generally in favor of "birthright" citizenship, but I'd like to get the gray areas out of the law. It clearly doesn't include everyone. So who does it not include? Can a pregnant couple sneak across the border to give birth in the US just so the child can become a citizen, so that they, as the parents, can live here legally?
I think it's fair to say the parents have to be here legally for it to qualify as "birthright". And I think that's possibly the right line. If they're here illegally, they're certainly not as subject to US law as citizens are. They can get pulled over for speeding, or prosecuted for murder, but if they were completely subject to US laws, they'd be deported.
If they're here on valid work visas, and they have a child here, fair game. Stamp the birth certificate as a citizen of the US. If the parents aren't here legally, stamp the birth certificate non-citizen.