1. Anyone born in the US and is REGISTERED is considered by the US to be its citizen (I mention registered, because there have been cases of people born on farms, not having birth certificates and having a hard time later on in life - after 18 - proving that they are US citizens when needing documentation - believe it or not this still happens).
2) I say this everytime this subject comes up. No country gives any real thought to what any other country does regarding its own citizenship laws/requirements. Germany has its laws, and many tens of thousands of Turks have "renounced" their Turkish citizenship in order to become German citizens. Guess what, they can get their Turkish passports back the next day as Turkey does not allow its citizens to permanently renounce citizenship (Once a Turk, always a Turk). Many countries (such as India) have similar provisions.
3) The case for the "back door" green card that 747 made is quite difficult to pull off these days, and not as successful as it used to be.