Kleon writes:
Anyone hatching a plan to destroy the United States with their progeny 50 years down the line could just as easily become a citizen first, therefore making the child a natural born citizen under even the strictest definition.
And that "strictest definition" would be THIS ONE provided by the Supreme Court in Minor v Happersett:
MINOR v. HAPPERSETT, 88 U.S. 162 (1874)
“The Constitution does not in words say who shall be natural-born citizens. Resort must be had elsewhere to ascertain that. At common law, with the nomenclature of which the framers of the Constitution were familiar, it was never doubted that all children born in a country of parents who were its citizens became themselves, upon their birth, citizens also. These were natives or natural-born citizens, as distinguished from aliens or foreigners. Some authorities go further and include as citizens children born within the jurisdiction without reference to the citizenship of their parents. As to this class there have been doubts, but never as to the first.
Do you not agree?
Among the definitions commonly brought up, yes, I think that would be the most strict. It's also one I don't believe anyone besides birthers really accept.