Because of the "and subject to the jurisdiction" part of the 14th Amendment. Foreign diplomats enjoy immunity from our laws and cannot be prosecuted if they violate them unless their home country allows it. They are not subject to our jurisdiction and because of that if they have a child while here that child is not a citizen.
OK... thats step 1. What about a foreign tourist who has a baby here while on her tour. Is THAT child an American natural born citizen for purposes of the Presidency? If not, why not?
I was hoping for assessment from mlo... Im still awaiting that.