Is the 14th amendment such a law? It says those who are born in the US are citizens, and that those who are naturalized are citizens.
Of course, who is naturalized will be defined by law, and Congress has the constitutional power to make rules of naturalization.
You seem to be saying that if Congress doesn't pass a law that says persons born in the US are citizens, that the 14th amendment has no effect, and that persons born in the US aren't citizens of the US.
the 14th amendment controls the laws that Congress passes and places a limit on the congressional authority.