1) Plyler is a decision based on an extension of the equal protection doctrine. I agree with that.
2) Your argument about who has the right to decide origin, however, stems from the Federal Preemption doctrine. That is, the Congress has made that the sole province of the Federal Government. (And yes, that determination of status could be changed by Congress.) Under Federal preemption doctrine, a state cannot enter that sphere of the law because in essence, it is solely occupied by the Federal Government.
3) Let's get to the heart of the confusion here. You insist, rather steadfastly, that a state would not be able to check immigration status because that is a determination of "origin," which it cannot do. I have disagreed. As you recall, I have said that there is a difference between seeking proof of origin, and making a determination about legal status.
As you are probably aware, a number of states, under state law, do require proof of citizenship or legal residency for certain benefits. For instance in Virginia one cannot get a driver's license from the State without -- you guessed it -- PROOF of U.S. Citizenship or lawful residency. The reason for this is simple -- Virginia is not determining citizenship, it is requiring proof thereof before permitting a benefit. Just one example.
Well, technically, the Constitution has made it the sole province of the federal government, and I believe it has been interpreted as to allow that power to be delegated to the states.
As you are probably aware, a number of states, under state law, do require proof of citizenship or legal residency for certain benefits. For instance in Virginia one cannot get a driver's license from the State without -- you guessed it -- PROOF of U.S. Citizenship or lawful residency. The reason for this is simple -- Virginia is not determining citizenship, it is requiring proof thereof before permitting a benefit. Just one example.
Yes, I am well aware of Virginia's "Legal Presence" law. You certainly can't point to the existence of a state law that's only been in effect 8 months as proof that what they are doing is constitutional. I maintain that unless they have such authority from congress, if such a law is challenged it will be struck down by a federal court. You sound to be too intelligent a person to be putting all your eggs in this basket.
More on Virginia's Legal Presence law, I will give you this - it is rather amazing that there are no reports of litigation involving this law. Normally the ACLU and the usual bunch sue before a law like this even takes effect. Of course, I'm guessing on something to happen after the election.