although I agree w/ the NAP. You seem to forget about property rights. If I own property, does that not prohibit me from allowing people to cross "imaginary lines?" Can I not discriminate who I allow onto my property? You're missing the only real function of the state - to protect my property rights consistent w/ the NAP.
Here's a quick post against forced immigration:
http://bionicmosquito.blogspot.com/2015/08/hoppe-and-immigration.html