I think this is a correct extrapolation of "anarcho-capitalism" (zero state) rather than "libertarianism" (minimal state). The minimal state approach could in principle keep a market balance by breaking up monopolies, and generally preserving basic human rights. It's the zero-state approach which is likely to lead to "firms" owning "territories" and exerting monopoly force within those territories (ie a return to a patchwork of states, though no longer called states).

Intriguingly, on anarcho-capitalist principles, such a firm would be entitled to do whatever it likes with its territory including defining very one-sided contracts to make use of it. Contracts like "Anyone who enters or stays in the territory becomes the firm's property, as do any of their offspring; anyone who leaves any form of matter in the territory accepts that it becomes the firm's property". And if you don't accept that contract, the firm denies permission to use any matter in the territory, such as food, water or air. Alternatively, the firm could - if it chose - define other forms of contracts, for any sort of social organisation it preferred : liberal democratic, socialist, communist, Islamic republic, whatever really. So under anarcho-capitalist principles, a division of the world into state-like bodies, defining whatever laws they like within their territories, is perfectly legitimate and acceptable. Since that is the world as it stands, I don't see what the anarcho-capitalists are complaining about.