America's strength has long been its ability to collect the world's best and brightest and mash them together in the relative economic and social freedom of their nation, and to suddenly shut out 95% of the world's greatest minds for not living in the right country is counterproductive. 

The fact that Canada does not do the same (in fact, we lose them to the states) is one of the reasons we're a relative economic backwater whose highest economic value is a deposit of sticky sand.