Anchor baby's are native citizens by statue (or "man's" law, not by way of nature or natural law). Actually, anchor baby's have the possibility of having triple citizenship at birth. U.S. citizenship by way of being born in the U.S., foreign citizenship from country B inherited from their foreign national father and foreign citizenship from country C inherited from their foreign national mother. That scenario, of course, assumes the mother and father are citizens of different foreign country's. Definitely a possibility.
Therefore, it's impossible that native born citizens (ex. anchor baby's) could be considered "natural born citizen's" as they have the possibility of multiple citizenship's and multiple foreign entanglements/foreign allegiances owed.
Houston, we have another winner!
A Treatise on citizenship, by birth and by naturalization, with reference to the law of nations, Roman civil law, law of the United States of America, and the law of France; including provisions in the federal Constitution, and in the several state constitutions, in respect of citizenship; together with decisions thereon of the federal and state courts (1881)