Literally medallions and literally the mafia? Not as far as I know. But most cities restrict supply of taxis to keep prices high and fix prices as the behest of the taxi industry -- in addition to all of the other fun things the taxi lobby does.

When Seattle built the Link light rail system, it stopped 1 mile shy of the airport because the taxi drivers didn't want the competition. Fortunately public outcry shut that down, but it's pretty rare that the general public gets upset enough about an issue to overcome the power of a specific interest group (yes, this includes Uber as well!)

There's plenty of literature to explain why price fixing and limiting supply/licensure is bad. There's no competition, no incentive to improve or provide a premium service. There's no reason to provide service in far-out areas where it might be hard to find a return fare. There's no reason to provide service in less "desirable" (read: minority) areas.

Of course, there are problems with the Uber model, too: Surge pricing being one of them. Some people think it's gouging, some think it's the right solution to provide supply for excess demand.