if private property owners have a right to form governments, they have a right to form borders, as an adjunct to their private borders. if you're against borders on principle, you also deny the legitimacy of government per se.
the government and the public spaces over which it has control are just the designated spaces of property owners to be overseen by common consent and laws. if you acknowledge those laws and governments as legitimate, then you acknowledge the right of a nation to formulate its immigration policy.
if you deny that right, you deny the legitimacy of the government.
you seem to be upholding the legitimacy of the government (you're not anarchocap) while denying the legitimacy of the border.
you're the inconsistent one!