I don't see how you can oppose free immigration without at least indirectly supporting the existence of a coercive state. I've read what (paleo) Rothbard and Hoppe have to say about it, but their argument (essentially, if all land were privately owned, "immigration" would require permission from the landowners) ignores several important facts.
In "Nations by Consent," Rothbard claims that under a "pure anarcho-capitalist model" "no land areas, no square footage in the world, shall remain 'public'; every square foot of land area, be they streets, squares, or neighborhoods, is privatized." There are numerous problems with this argument.
- All land would not necessarily be privately owned just because it wasn't owned by government. Some of it would be unowned. Trails and roads that were in common use before the abolition of the state could not justifiably be seized or homesteaded by one person or entity. Additionally, not every scrap of remote desert and every lonely sub-zero mountaintop is going to be homesteaded.
- The presumption that "no trespassing" would be the default position on all private property is not born out by reality. Many private property owners allow for recreational use and travel across their lands even now, and there is no reason to assume that this would change in a free society.
- Most immigrants are welcomed by employers, landlords, businesses, churches, and other private entities even in a statist environment, and would likely be even more welcome in a free society.
- Even if Rothbard and Hoppe were correct that all land would be privately owned, that all property owners would universally ban travel across their land, and that employers, landlords, businesses, and private road owners would not welcome certain prospective customers based on birthplace; that still would not justify limitations on travel imposed by a coercive state on property illegitimately claimed by the state.
The other anti-immigration arguments put forth by "libertarians" typically relate to the welfare state and the notion of "culture." The first stems from a valid complaint against institutionalized theft and redistribution, but ultimately falls flat because no one is any more or less entitled than anyone else to receive stolen goods. Blaming immigrants for the crimes of a coercive state is neither reasonable nor fair. It should also be noted that immigrants and foreigners are not immune to the hidden taxes imposed by coercive states which cause inflation and price increases resulting not from market factors, but from state-imposed taxes, fees, and regulations. Despite the divisive "only half the people pay taxes" rhetoric, no one on earth is free from the negative financial impacts of state action.
The "culture argument" is simply an attempt to use state coercion to enforce one's preferences and is no more justifiable than government-imposed segregation or any other such policy. No one has an inherent right to be surrounded only by people who look or think like them, and it is even more absurd to believe that such a preference should be violently enforced.
In simple terms, the free movement of individuals does not typically constitute the initiation of force against others (the single exception would be that private property owners are not required to grant access to unwelcome guests) whereas immigration restrictions do necessarily constitute the initiation of force both against those whose movement is restricted and against those who desire to engage in commerce with these immigrants.