On the one hand, it is not possible as a libertarian to support a regulated immigration policy, since government itself is never legitimate.I don't want to argue with anarchists, I really don't. It's counter-productive. I want government out of my life, they want government out of their lives, we shouldn't have to argue about the little nit picky things like government legitimacy.
And then one of them goes and throws a bombshell like the above. For the record, there are two kinds (at least) of libertarians. One group freely calls themselves anarchist (technically anarcho-capitalist) and takes the above view. The other (far larger) group just wants less government interference in day to day life (Less government interference = more freedom) some of us freely use the label that Robert Nozick (that Per Bylund references in his piece) coined for us, "Minarchist"; which loosely translates into "The least amount of government needed". Mr Bylund himself must therefore be aware that his sweeping generalization is in error, but he goes on with the article anyway based on this erroneous assessment of Libertarians.
The reason that 'open borders' is the 'right way' to look at immigration policy is pragmatic, not idealistic. Pragmatically, the cost to 'close' borders is prohibitively high, just in monetary terms. The cost in lost privacy, freedom, etc. doesn't even bear thinking about (which is why a libertarian that advocates 'closing' the borders isn't one) Realistically, we have never been able to 'close' the borders, not even in a state of war.
Which is why we should just "let 'em in". Get whatever information the control freaks think we 'have to' have in order to track the new immigrants (fingerprints, DNA, retinal scans, whatever) and let them get to work. I don't have time for 'air-castle' arguments concerning natural rights and the ownership of the commons; those sorts of things can be saved for the day that the anarchists get rid of government. I doubt that I'll be there for that.