If you want to understand this you simply have to listen to the below excerpt from a planet money interview with Mark Zandi the chief economist of Moody’s Analytics and contrast that with the petit bourgeois, xenophobic attitude towards immigration that is prevailing in Europe:

and again, fundamentally we are fine. we can’t loose the sight of what makes our economy really tick though and that is: the most educated population, the best infrastructure and most importantly of all that we continue to attract the best and brightest from all over the planet, because as long as we can do that we are gonna be just fine.