Borders are Not Property, Authority is Not Indivisible.
The main reason I dislike nationalism: territorialism. The process of territorialization of political demesne has been a recipe for totalitarian sovereign states. Polities do not consist of rocks and streams, they consist of persons. There is no such thing as a ‘natural’ border and the actual boundaries of political units is actually the ambit of people who participate in its institutions. I do not believe in ‘national borders’, and not because of some anarchist principle, but because they are entirely fictional.
On the anarchist side, however, it is ridiculous to claim that anyone has clear title to multicultural parking lot cities or the vast uninhabited hinterland that makes up most of the planet. Europe has densely populated areas where even the forests are worked private property, I can see a case for exclusion of immigrants there. But in the United States this is nonsense. On the other hand I see that some local communities definitely do have some kind of right of exclusion based on, not territory, but the desires of the persons already living there. Yet the concept of territorial sovereignty undermines this by declaring all such regions, equally with vast tracts of Federal forest lands, to be under the jurisdiction of the Constitution and the police apparatus.
The ‘bordertarians’ fail because nation states and territorial sovereignty are fundamentally unlike private property and contract, and if anyone looked into the actual history of ancient China or medieval and classical Europe they will find that ‘muhBorders’ are actually a quite recent innovation. This is also paired with the nonsense that sovereignty should be indivisible, a pernicious outgrowth of Enlightenment rationalism that doesn’t like things to be organic and wants to draw straight lines over every map.