What is the theme in The Moon Is a Harsh Mistress by Robert A. Heinlein?

The Moon Is a Harsh Mistress depicts aggressive colonialism on the wane. Luna begins as a penal colony administered by a Warden. Inescapable, the prison needs no walls and bars and as convicts complete their sentences, they suffer no social stigma. There is no question of political rights, as the colony is administered from Terra. There are no laws, but social pressure and vigilantism keep good order. Loonies learn to act properly or are informally "eliminated." Luna Authority has evolved into an exploitative monopoly that spawns uncoordinated and ineffectual revolutionary movements, particularly in isolated, affluent Hong Kong in Luna (HKL), which becomes de facto autonomous by using only products grown or manufactured locally. An organization in Luna City invites political activist Wyoh Knott to address a rally and she calls for eliminating the Authority.