I hate this guy’s statement being declared orthodox libertarianism. Hayek is a much better source and Hayek’s position is laid out in this article.
You cannot have external free market contacts with another economy that does not have a free market internally. That goes for immigration as well. If Mexicans and South Americans lived in open, free and free market societies, they wouldn’t have to escape to ours.
Instead of escaping, of course, they are just bringing their problematic outlook to our society, trying to destroy the very society and markets that they came to enjoy.
Milton Friedman said, “You cannot simultaneously have free immigration and a welfare state.”