Libertarians on Citizenship

A few days ago, Ed Crane, president of the Cato Institute, wrote a piece on Ron Paul in the Wall Street Journal containing the following graf:

Which is not to say that Mr. Paul is always in sync with mainstream libertarians. His seeming indifference to attempts to prevent Iran from obtaining nuclear weapons, his support for a constitutional amendment to deny birthright citizenship to children of illegal aliens, and his opposition to the Nafta and Cafta free trade agreements in the name of doctrinal purity are at odds with most libertarians.

When did birthright citizenship become a tenet of libertarianism? I'm not being smarmy — I really have never heard a libertarian include preservation of our current citizenship rules as part of his agenda. Dan Griswold is Cato's point man on immigration and in all the times we've shared a stage, I've never heard him even address the issue. His piece in today's National Review Online, which recycles all the usual open-borders applause lines, doesn't mention it. (BTW, NRO readers don't seem to be buying what he's selling; the comments to Dan's piece are scathing.)

In fact, the only time I recall a libertarian addressing the citizenship issue (though not births to illegals) was Jacob Hornberger of the Future of Freedom Foundation. During a panel we were both on Hornberger was challenged that immigrants would vote for socialism; he responded that immigration and citizenship are separate issues, and that immigrants shouldn't necessarily be allowed to naturalize and vote (essentially, the position of the Know-Nothing Party).

Is there a standard libertarian position on the issue of citizenship for the children of illegals? On the one hand, if people are free to move across borders unhindered, then all immigration would be legal, so no problem. On the other hand, if open immigration were to proceed on the Gingrich model of guest-worker visas (not leading to citizenship), then I could see a move to change the citizenship rules so the children of such workers wouldn't get citizenship. (Linda Chavez has suggested as much, though she's obviously not a libertarian.)

I'm not trying to score a political point here; I'm personally ambivalent about the birthright citizenship issue and consider it of secondary importance. (Though CIS has published path-breaking work on the subject.) But if the head of the nation's leading libertarian institution, in the nation's leading libertarian newspaper, is criticizing the nation's leading libertarian presidential candidate about it, there must be some principled explanation (beyond just wanting to maintain an open-borders united front with the Left).