Ilya Somin has a thoughtful post on Volohk about immigration and its consequences. I find myself probably in a minority on this issue. I would think Eugene and Ilya would too, but evidently not, at at least maybe not. But I would think they would have, and I certainly do, the following problem. Suppose one considers oneself a libertarian; it doesn't matter whether you are soft or hard. Any sort of libertarian will do. Then you are asked whether you want to give somebody from outside your political body the power, via the vote, to make decisions that will apply to you, and that person does not share your attitude toward your rights. Indeed, he thinks there's nothing wrong with a big state, lots of welfare benefits, and so on. I would think it would be an easy question to answer -- the libertarian would say, uh, no thanks; you should go to a country more in line with your political beliefs.
So a libertarian would think everybody has the right to go wherever they want and be a citizen, but not think they should be able to exercise their rights, or rather they would not have those rights, once they got there. I don't think the federal government has, for example, the right to take away the rights of citizens to arm themselves. But immigrants might, and if there are enough of them, gun control would have a better chance of passing. And eventually, being approved of the by the Supreme Court. Many other examples could be thought of.
I am all for immigration, so long as the people who come here share my political beliefs. Some will, but most will not.