“Passing a STATE law saying someone is not a citizen of the United States is absolutely unconstitutional.”
The law would INTERPRET the 14th Amendment, not replace it. It could be written to say that for the purposes of state benefits, the state only recognizes those born under the jurisdiction of the USA as citizens. Or it could be written as requiring the deportation of anyone without immigration paperwork who is not a citizen IAW the Constitution, and then expand that to specify that the children of illegals are NOT under the jurisdiction and thus subject to deportation.
There is no chance Arizona will pass such a law, so it is a bit academic. But there is nothing in the Constitution or that I’ve seen in court cases that REQUIRES the child of an illegal to be considered a citizen. In fact, I can think of several SCOTUS decisions that would support the reverse. Decisions such as Perkins v Elg, or WKA all make the point that the parents were here legally at the time of birth.