I really wish I could believe in your story, but you're sweeping too much under the rug.
You talk of the towns as rational decisionmakers, but they aren't - they're just collections of rational people. Your argument for anarchy assumes a degree of coordination that anarchy itself rejects.
My story was just a simple contradiction to yours and was not meant to be the go to guide for voluntaryism. It was meant to counter your primary argument. If someone acts maliciously in a trade for their own benefit and is not mutually beneficial, then it is easy enough to just not agree to the trade. The malicious actor is then barred from future trades and suffers the consequences.
But even throwing my little story out the window, just take a look at the world right now. We have a bunch of independent countries all acting for their own benefit. There is no world government telling each country how to act, so they do so according to their own needs. There are trade agreements and the UN etc., but what happens if countries don't follow the rules or act disreputably? Sanctions. AKA refusing to trade. If this can be done on an international scale, I would think it can be done on smaller scales between people, cities, states etc.
I love these ideas but the biggest flaw to anarchy/voluntaryism in my mind though is protection from violence. What is to stop groups from just using violence to impose their will on citizens again and bring people back into coercive governance? Or if groups do build their own protective forces to prevent this, what is to stop some rogue commander to stage a coup?
The old chestnut, 'But wouldn't the warlords take over?'. No, they wouldn't because voluntary agreements with multiple competing security providers would exist, and those providers would have agreements with each other when violent incursion affects each other on a scale that is outside the limits.
Note also that historically, such as the war of independence and the civil war, it was a mix of regular and irregular forces that came to win in the end. This is something that can only happen when anyone with the will to pick up arms and learn how to use them and who makes the effort to be communicative with the more formal, organised forces near them, can produce defensive capability that can repel all but a greatly overwhelming size of force. The bigger the force, the greater the chance that more people from a wider geographical region would get involved.
Capitalism has the advantage that people who adopt it as strictly as in the anarchocapitalist form of it, are both wealthier and more peaceful. It would be extraordinary for an outside force to come into play or even an internal force that does not understand that production and productivity are the key to winning wars, would not be less equipped at waging war. The USA was the main winner of World War 2 not because of anything other than its long period of relative peace and capitalism had provided far more resources and capital in the form of productive capability, that the soldiers had more power per person than either side of the enemy.
The warlords wouldn't take over because they'd be so tightly organized and intertwined with the economic order as to be indistinguishable from a government. ;)