The main idea: Though only a second-best alternative to a nuclear umbrella, a reformed Militia system could still afford weak defenders a way of imposing high costs on much stronger aggressors, with obvious implications for non-territorial defense in a Free Society.
1. The rationale of Militias
1.1 From the position of a weak believer in the ability of a future Free Society to credibly defend itself by conventional (non-nuclear) means, the idea of a Militia begins to look attractive. If non-territorial private defense agencies would probably be underfunded due to public good problems, if territorial entities could not be large enough to property defend themselves due to rational calculation issues, and if, for the time being, a proper credible nuclear second-strike capability is very expensive to procure (that is, too expensive even for China), than one is left with precious few alternatives when it comes to defending against a stronger attacker.
1.2 And indeed, a Militia system along Swiss lines is held in high esteem by some libertarians, who often compare it to the alternative of behemoth, uber-costly conventional armies creating problems too well-known to discuss.