Hold on - what is “natural” about the requirement for two citizen parents?
English common law was also built on Natural Law - to them, just being born on the soil made one “natural” born.
How many Natural laws are there? Did American founding fathers change Natural Law - in which case why would it be considered natural? Or did they simply recognize a different Natural Law?
The problem with Natural Law is that no one can authoritatively say what it is. Or rather, that anyone can say it says anything they want. Hobbes identified 19 Natural Laws, but a two-parent requirement for natural-born citizenship wasn’t among them. Theologians argue that natural law is that ordained by God, but I doubt you can find a religious scholar anywhere who can find much Biblical support for a theory of the transmission of citizenship across generations one way or the other.