I have received quite a few comments on my 12/8 article about the Libertarian Immigration Conundrum (discussion here). A common argument against open borders goes something like this: "If X million [non-wanted] immigrants would occupy your country, would you then be so prone to advocate 'open borders'?"
The argument is usually claimed to be economic, since it emphasizes the unbearable "social cost" of immigration to the general state welfare system or immigrants as a threat to the social structure of society and how "we do things." But the economic dimension often claimed is a mirage rather than a real argument, at least from a libertarian point of view where individuals are more important than groups or collectives. The problem with this "economic" argument is not that immigrants use services and benefit from "rights" mandated by the state without having first paid taxes. Being an immigrant is not the real problem if this were a true economic argument; the problem should be that immigrants are often consumers of public services but not contributors to the collective good supplying these services! That would be an economic argument.
But if this is what you're saying, that immigration is a threat to our (whatever "our" means here, I do not know) welfare system, we would have to see the full picture and not only discuss immigration. To "protect" the welfare system, one would also have to advocate things like state birth regulations akin to the program in the People's Republic of China, since children (and their parents) do use a number of welfare services without paying for them.
The similarity to the economic problem of immigrants is striking: children are not a part of the working (tax paying) society and they are generally more vulnerable than grown-up citizens. They need schooling in order to speak the language everybody else speaks; they need education to understand underlying social and cultural principles of society; they need health care and use other public services such as roads, playgrounds etc. without paying any taxes.
The economic argument against immigration has really nothing to do with immigration per se. (Also, immigration is usually a net benefit to society rather than a cost: immigrants tend to work harder and use less public service than natives, who are rather spoilt or indolent in comparison.) The economic argument is in essence an argument discussing two kinds of people in state society: those being net consumers of public service and those being net contributors.
Net consumers are technically parasites living off others, while the other kind are people being used and abused for the sake of the parasites. Some immigrants are part of the parasitic collective, while others are not. Most children and elderly are social parasites (net consumers), while working people are net contributors. Sick people are consumers, while healthy people are contributors; poor people are consumers, but wealthy people are contributors; solitary, individualist people are perhaps consumers compared to people with a strong sense of family, who solve their problems without ever engaging the state.
I admit that immigrants are easy targets — they do not look like "us," behave like "us," speak like "us," and they may not even smell like "us." But what does this feeling of alienation have to do with costs of state welfare? Probably nothing. What you are doing is simply disguising your personal xenophobia in a language of economic reasoning. And what that has to do with libertarianism I simply do not know.