I have faulted libertarians (I personally prefer the classical liberal label) for not being sensitive to the issues that seem to them to be on the periphery of such greater issues as the immigration problem in America. I blame it on many things, one of the common things being that libertarians who openly espouse a support for the open borders ideology tend to be insulated by their position of relative comfort from its immediate effects. Better police protection, less competition for jobs (typically no competition), none of the unpleasantries.
At a potential cost of $126 billion, it's no laughing matter to the majority of Americans who do not live a very affluent lifestyle. Their tax dollars will go to pay for the benefits of low and no skilled workers whose labor has hardly benefited them except in some sort of academic economics sort of way. The bottom line is that there are two sides to this issues: those who benefit and those that do not. The former are fewer than the latter.
Libertarians wonder why they have been steam-rolled since 9-11 into the ground by the blundering Bush Administration, but it's no secret: libertarians are perceived as being impotent ideologues on matters important to preserving a free society. Disgusting, baseless rhetoric such as casting all opponents of illegal immigrant as buck-toothed, yeehaw hillbillies who hate all "dem G-d damned fereners" has basically handed the battle right over to our enemies. It is easy to be a smug, cosmopolitan libertarian when you aren't one of the low-skilled Americans or even, for example a construction worker, who is going to lose his job to a desparate illegal immigrant.
I'm one who would often call myself some form of libertarian (usually with "Messianic..." or some appropriate adjective).
the salient comment here about "open borders" is that it wasn't originally the 'openness' that was the problem - it was the perverse incentives of a socialist welfare state!
Back when we attracted people who came to "breathe free", worship, and employ their own energy and intellect to build a better life for themselves and their family, we were in pretty good shape.
Now they come instead for a piece of the gravy train, and perhaps to import a bit of nuclear or bio-weaponry to boot...
I don't know. The first wave of immigrants did a lot to bring statism to this country between attitudes and their service in the Northern war machine. I think that limited immigration can also have the added benefit of forcing other countries to change and become more like the liberal country. Since they can't flee, they have to build a little slice of liberty in their own homeland.