That doesn't hold water when workers work for companies with foreign customers. One way or another, you're competing with foreign engineers: if they can't work for US companies, they'll work for their local companies in the same markets. For example, Google is now practically the global search engine, but it's an American company making tons of money off foreign users. If only American developers were allowed to work at Google, it's possible many more country-specific search engines would pop up (many already exist, but they're not as popular).