I agree with your broader point, but if the United States has a comparative advantage in entrepreneurship, it's not actually zero-sum.
That is, if the American legal system, venture funding, etc., combine to offer a foreign entrepreneur a better likelihood of building a successful company there than in her home country—and there's some evidence that that's often the case—then letting her emigrate to the United States should be a net gain for the global economy.
True, but for every non-us company that creates broad democratic institutions and enforceable contracts, then that countries comparative disadvantage shrinks, probably towards a meaningless point.
Look at India - democratic, enforceable contracts, and vast internal Market. Sound familiar?
Go to New Mexico, or southern California you will find tired, poor huddled masses.
That is, if the American legal system, venture funding, etc., combine to offer a foreign entrepreneur a better likelihood of building a successful company there than in her home country—and there's some evidence that that's often the case—then letting her emigrate to the United States should be a net gain for the global economy.