Imagine you could talk to the founders. Either hop into a time machine to appear before the continental congress, or zap them all into existence here and now. How do you think they'd react to "Of course it's natural that our nation should fill with Mohammedans and Africans and Cental and South American mestizos, because the United States is just a neat idea."

A piece of paper that says you're a citizen does not make you magically turn American. American soil isn't made up of magic dirt that turns people American when they come here. The problem is the vast majority of them AREN'T WITH US, and they never will be.