67% of everyone in the United States who entered Science and Engineering between 1995 and 2006 were immigrants. Almost 25% of all international patent applications from the US name foreign nationals as inventors.
US immigration policies prevent an absurd percentage of skilled foreigner workers from becoming citizens, so thees people return home with their skills. Their talent then benefits India, China and Canada instead of the US.
The US needs to keep growing to survive its debt load. The way for us to grow is innovative science and technology. Is there anything above that makes any sense?