At the time the U.S. Constitution and its natural born citizen clause was adopted, there was no such thing as dual citizenship. You had to give your allegiance to one sovereign. Britain and the British Empire went further by demanding allegiance to the British sovereign for a person’s entre life, with no recognition of any right to adopt another citizenship. A person born in Canada was born with Canadian citizenship. The U.S. Government does not officially recognize a right to dual citizenship or multiple citizenship. Instead, the Supreme court of the United States has compelled the Executive branch of the U.S. Government to not take away the citizenship of persons exercising foreign citizenship in addition to U.S. citizenship, except in those statutory circumstances where a person’s foreign citizenship is excluded. U.S. citizenship acquired at birth in a foreign sovereignty without two U.S. citizen parents does not qualify as natural born U.S. citizenship.
Citation, please.
Well before the Constitution was written, it was recognized that citizenship at birth could be based on the citizenship of the parents instead of simply the location of birth. Diplomacy and commerce often had need for lengthy foreign postings, which inevitably meant that spouses would come along and that there would be births abroad. It was not thought that a child could fairly and properly be denied the citizenship of its parents simply because the child was born abroad.
This principle was recognized and followed in the citizenship laws of the first Congress. Such enactments are considered authoritative by the US Supreme Court due to their closeness to the drafting and adoption of the Constitution.
And, if you think it through, you may come to believe as I do, that this point is also connected to the rationale against anchor baby citizenship. The mere happenstance of birth on US soil should not be permitted to confer citizenship when the parents are here illegally. The citizenship of such children ought to be based on their parent's citizenship, not on having hopped the border.
Which law states that both of your parents need to be U.S. citizens for you to be a "natural born" citizen? I would think there would be all sorts of unintended consequences that would affect situations where the paternity was unknown or perhaps a rape took place, etc...