I distrust the underlying forces structuring light new businesses like Uber. When the entry cost is too low, people have no reason to put real effort. On the other side of the spectrum, Parisian cabs suffer from too high entry cost, AFAIU they have to work "hard" for a long time before they can reimburse the licence. And that contrast is what's causing the violence.

Okay I understand. The rating system does a good job to resolve that issue. Under a 4.7 and you are not allowed to drive on the system (IIRC). Personally I've experienced, and talked to ~50+ people, who have experienced a far superior service using Uber than alternatives.