Others, like Ron Paul, argue the lure of the social welfare state. (Hoppe rightly argues the social welfare net is a separate issue.) The basic argument is fleshed out in this quote from Milton Friedman:
There is no doubt that free and open immigration is the right policy in a libertarian state, but in a welfare state it is a different story: the supply of immigrants will become infinite.(Note that Friedman was not a restrictionist; he specifically approved of illegal Latino immigration.)
But the line "the supply of immigrants will be infinite" is fairly generic; for example, the Trump proxy in a recent SOHO debate used it to rationalize restrictions. The idea is that the other 95% of the global population would quickly overrun the native population and transform the country to something different, without our consent.
Now first of all, I want to provide a personal anecdote that illustrates, from both directions, how unrealistic this being overrun scenario is. In 1995, I worked at a Brazilian client location in Sao Paulo for a few months (I thought it would be for 3 weeks). Among other things, I was dating this beautiful Brazilian woman. (Not bad given the fact I knew little Portuguese going to Brazil, and my lady knew little English. I don't even remember how the topic came up but my project manager told me that he could get me the equivalent of a 6-figure job offer with the client, well-above what I was making and would make for comfortable standard of living. Don't get me wrong; I loved visiting Brazil, and I love the people there. But my family and friends are back in the States a continent away; I love the freedom and the country, our culture and customs. As for girlfriend, I would have loved for her to join me in the States; I probably would have married her. But she had no interest in coming to the States (beyond an occasional tourist visit): her family and friends were in Brazil; she loved her country: the flip side of my experience.
I don't claim that my anecdotal experiences are generalizable, but I do think there's a risk in relocating to a new place with strange new customs, language, and culture: how well will you be treated in your new homeland, can you find steady work; you are leaving your comfort zone, you may never see again your family and your old friends. Yes, it's an easier decision if you are fleeing political oppression, like Hitler's "final solution".
I can't interview my great-grandparents on both sides of the family who emigrated from Canada in the late nineteenth century. I know certain aspects of the Quebec diaspora, e.g., large Catholic families ran out of room to sustain individual farms. New England became a lure for many French-Canadians looking for a better life, including farmers and loggers, not to mention the lure of jobs at the textile mills of Fall River, MA, where my own folks were born in a thriving Franco-American community. (The textile mills have long gone away, with Southern and other competition.) My maternal grandmother was a weaver and proud of her skills; my grocer grandfather wanted her to be a housewife, proud of his ability to provide for her. But make no mistake; working at the mills was a hard life. And of course there was no social welfare system. Franco-Americans pride themselves on a hard work ethic, probably considered it a loss of face to take charity.
So let's be clear: the immigration boom during the nineteenth through early twentieth century occurred without a social welfare state and the federal budget was small; we also didn't see unlimited people coming. This was under a fairly open immigration system (with some ugly anti-Asian exceptions and/or unofficial caps). We have some significant expensive access problems for most of the global population outside the Western Hemisphere. Since about WWI and its aftermath we've seen an economically illiterate quota system, which remains intact to this very day; it creates artificial shortages, even as our high tech industry seeks to recruit global talent to accommodate growth initiatives. Even if we tripled our annual quotas, it would only mean like something 1% of the American population. Having to wait 15 or more years is an abomination. And most empirical studies I've seen show significant economic benefits to increased immigration.
I see the right to travel and to migrate as an essential construct of freedom. I see restrictions to immigration as an abomination to the ideals under which this country was founded. Almost every libertarian think tank--Cato Institute, Reason, Adam Smith Institute, etc.--advocates an open-immigration perspective. I've often cited Cato's Alex Nowrasteh. Bryan Caplan's Open Borders, and Benjamin Powell, among others.
