de Sola Pool's book 'Technologies of Freedom' gives an excellent description of issues of monoloplies and their motivations. He describes a scheme that I think was adopted in Boston. The scheme was to grant a cable monolopy but require the cable owner to lease half of the cable capacity to a competitor at some prespecified price. There was thus competition between suppliers of programs. The arguments for a natural monopoly were accommodated (Space on the phone pole, cost of laying cable) and yet competition was achieved. That was one of the few books that I have read that actually changed some of my opinions on economics. The author described why rational, non corrupt regulators might grant such a monopoly. He did not imply that such monopolies were not corrupt.