On a June morning in Los Angeles, more than 100 cabbies rallied their cars around city hall, looping the 27-story granite building in a horn-honking protest against what they called "high-tech bandit cabs." The day before, the city had issued a cease-and-desist letter to three start-up firms that provide ride-sharing services--nonprofessional drivers, linked by smartphone apps, who will chauffeur you in their personal cars at prices that undercut local cabs. "It's making us nervous," one driver told a local TV reporter. "They come and steal our fares through these apps."
Steal? Perhaps we should use a more polite term: disrupt. The...