Sources: SF Examiner, Lyft and Sidecar, Fox News, California Public Utilities Commission (CPUC) [PDF]
quote: But if you're driving in your car solely to give someone else a ride, that represents an additional person on the road. If you're driving around looking for someone to give a ride to, that represents an additional car on the road. The roads only have a certain capacity, so beyond a certain point any unnecessary driving is detrimental to other drivers who have a legitimate reason to be on the road. That's why taxi services are regulated - to limit the number of taxis on the road.