Well that’s easy: government itself proves that social cooperation is possible without the state, since there’s no third party to enforce contracts among the individual members who make up the government. (See Cuzán and Plauché for details.)
Unlimited secession rights (i.e. ethical claims) would require ethical arguments, no?
And their cases have been embarrassingly awful. There are plenty of bad arguments given in favor of libertarianism, but the analogy between taxation and slavery is not one of them. As Christopher Wellman writes (p.5):
Thus, when one pauses to look closely at the comparison between slavery and political imposition, one sees that it is surprisingly difficult to distinguish between the two. The key shared element is nonconsensual coercion. This feature that makes slavery impermissible is also utilized by all governments and thus places the burden upon any of us who are reluctant to label all political states unjust. Thus, the analogy between slavery and political coercion appears not only apt, it is helpful insofar as it motivates the central and most important question of political theory: Why not be an anarchist?
Not for me. As a libertarian, I want society to be, well, libertarian. In fact, the whole point of advocating competition in legal systems is to achieve this end.
Um, isn’t this the whole point? Anarchists are trying to mold society to conform to our preconception that there shouldn’t be a monopoly on law.