First, a question: dear reader, can you point me to examples of bloggers or other writers openly and confidently changing their minds? I will demonstrate what I'm looking for.
Two weeks ago, I lost almost all sympathy for libertarian views. Legalize marijuana? Well, of course. Restrict immigration? On what grounds? Then I came to understand anarchism better.
The government is not legitimate. No decision it makes is moral. It has the right neither to condone nor condemn immigration controls.
True freedom is having the acknowledged right to make either or any decision, if it is about your own property. It is no more immoral to bar settlement on your property than it is to have rules against bubble gum.
Who exactly can claim legitimate title to the G8 borders in dispute? As far as I can tell, nobody. The ones in control took the borders by force, negating their own claims, and the ones they wronged are dead. But, if someone did perform the necessary trades to own an entire country-sized land mass...well, morality isn't scale-dependent. If they say you can't cross, you can't legitimately cross, end of story.
Even assuming I'm wrong, and that the mythical 'public good' security is necessarily or inevitably supplied by a state, the simple fact that libertarians find such a minarchist state legitimate gives them the right to secure the libertarian against any harm they see fit to. If their evidence shows that immigration is harmful or has a notable downsides, they can secure the citizen against it. If their evidence shows marijuana causes externalities strong enough to justify the cost of prohibition, then they can secure the citizen against potheads. Security can't be neatly chopped up into military and non-military. Negative externalities recognize no such distinction.
(This is one reason I buy the argument that minarchism is unsustainable. The night-watchman state has an interest in and the ability to use negative externalities the way USG4 uses the commerce clause to justify unlimited expansion.)
While I happen to think pot (and most drugs) can't possibly cost more than the war on drugs, in a minarchy the question is one of cost and benefit, not of morality.