Is there really a lack of people in the USA today who want to start companies? It might be a zero-sum game -- X dollars available for startups; if you let in a bunch of people, the startup dollars will go there rather than to people already here.
But that is where the beauty of having the market decide comes in. If a person from India but founding a company in the US has a better idea, then the money SHOULD go to her. That is best for the investors, and it is best for America, because a better idea will build a better company that will create more jobs.
The zero-sum-game fallacy is at the heart of every single immigration debate I have ever followed. The size of X depends primarily on expected returns. That's how investing works. So if you assume that X is constant for any particular country, you're implying that returns are independent of how many good founders are available. I think that's not a reasonable assumption to make.
