In Libertarianism in One Country, Derbyshire explains why it makes sense for liberals, who favor the welfare state and aggressive multiculturalism, to favor expanded third world immigration; but argues that libertarians are nuts to want a more open immigration policy, since it's self-defeating. (Thanks to Justin Raimondo for the link).
Derbyshire could have benefitted from including the thoughts on immigration of various explicit libertarians, such as Hoppe, Rothbard (e.g., Nations by Consent: Decomposing the Nation-State), Block, and others, and the JLS symposium on immigration--but still an interesting read.
