The United States current policy of granting American citizenship to any individual born within its borders encourages pregnant foreign nationals to travel to the United States during the final trimester of their pregnancy for the explicit purpose of delivering their baby here. These mothers enter the United States illegally, whether explicitly so, or because they are misusing tourist visas which are not intended for child birthing purposes.
Some of individuals will even receive tax payer funded emergency insurance to cover the cost of their child's birth.
Citizenship should be granted if and only if the mother is here because she is (1) an American citizen, (2) a legal resident alien, (3) here on a non-tourist visa and has been in the United States for a period of more than a year.