I hold a mix of views but I'm more in the libertarian / autarchist / anarcho-capitalist end of the spectrum.
I remember reading an anarcho-capitalist SF book in my teen years where everyone was automatically made a citizen after six months residence. No muss, no fuss.
Really though, if you support free markets/free trade, you should support free movement of peoples. It's the only logical check that workers have on the rights of employers in a libertarian system. Bosses are free to set up shop wherever they can get the lowest wages, and workers are free to migrate wherever they can get the highest wages.
IIRC, it's even explicitly in The Wealth of Nations.