> Unregulated markets can result in a number of situations that limit people's opportunities significantly. Monopolies are a clear example and various externalities can also have significant impacts on commerce.

Could you name an existing stable monopoly that is not a state-granted monopoly (i.e. a monopoly, that is not associated with government regulations, subsidies, grants, medallions, quotas and other things that have to do with regulating the market by the government), yet is capable of preventing other players from entering the same market?