Well, no. A group of armed criminals is clearly not the only way to enforce that. For it's immoral to provide anything, including life/property protection, via use of force (taxation), and artificial monopoly isn't such a good thing, either.

Private protection is certainly possible and is definitely more moral than sovereign monopolist protection provided through means of aggression. See http://www.daviddfriedman.com/Libertarian/Machinery_of_Freed...