With this statement Mises had already crossed the line separating classical liberalism and Rothbard's private property anarchism; for a government allowing unlimited secession is of course no longer a compulsory monopolist of law and order but a voluntary association...once admit any right of secession whatever, and there is no logical stopping point short of the right of individual secession, which logically entails anarchism, since then individuals may secede and patronize their own defense agencies, and THE STATE HAS CRUMBLED.
Recently, I have become rather intrigued by the idea of "secession." When I say secession, and even when Hoppe says secession, neither of us means repeat the 1860s. The strategy used by the Confederate States of America didn't work, and this same approach to secession should not be tried again. What is meant by secession now is to first change the minds of individuals. Secession begins as an ideological war. It is about getting people to see that democratic institutions, in fact all government institutions, are illegitimate. No government has the right to claim legitimate consent because no government is voluntary. Then, secession begins at the local level. Towns, villages, small regions. The idea of secession is to slowly destroy the state from within by creating hundreds of pockets of resistance.
I should also point out that secession, in the modern sense, has nothing to do with violence. I abhor violence; I want to live in a society of voluntary cooperation. Organized violence has its provenance in the state. So a secessionist movement must never engage in violence--to do so would be hypocritical. You can't say: I want to set up a peaceful voluntary society and then go about launching wars of aggression to get it. A consistent philosophy of secession then says that the means and the ends must both be non-violent and non-invasive.