If you argue that intellectual capital is becoming relatively more important than money capital, we must create a climate that attracts it. America is the only country that renews itself with this energy, skill, and intellectual capital that migrates to our shores. That's why we will survive and prosper where closed societies that keep people away from their borders will have a difficult time. A nation has the right as well as the duty to control its own borders. Without that control a nation is not in charge of its own destiny.
History is full of examples of nations being overrun by uninvited outsiders.
Some of the nations benefited from the infusion of new blood and some did not. In either case the destiny of the nation was taken out of the hands of the native population. The United States could have a relatively open immigration policy in the past when immigrants knew that a newcomer had to work or starve. That knowledge screened out a lot of people. Today, new immigrants come because they know that they can live better here than in their own country whether they work or not.