Carl: Why else would there be so much disagreement?

Because many people who claim to be libertarians, aren't actually libertarians, but rather believe in a toxic mix of small-government Constitutionalism and belligerently nationalist conservatism.

Of course, if that's what you believe, then borders have an obvious place in your philosophy: any mini-statist is going to be in favor of some border enforcement (since territoriality and borders are essential features of the state as such, and they defend the enforcement power of states); and if you are into a lot of mind-numbingly dumb ideas about the American nation-state, then these often lead to violently dehumanizing people from other countries controlled by different nation states, and invoking a lot of mind-numbingly savage nonsense about the "right" of that nation-state to preserve its national character, etc. How they think that they can square these ideas with a professed belief in "individual liberty" or even in "limited government" is really kind of beyond me, but as long as "libertarianism" is, for many, not the creed of radical individual liberty regardless of political identity or legal status, but rather some kind of code-word for a leaner, meaner state and hyperconservative American nationalism, there will continue to be people who convince themselves that it can somehow be done.

That doesn't make the question complicated. It makes their attempts to ignore or avoid the obvious consequences of libertarian principles complicated -- even downright acrobatic. But that's another kind of complication entirely.
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