No: Riots (or semi-spontaneous reactions as in Wisconsin) have neither positive nor negative features, and it is incorrect to discuss them as though they did. They are events, not systematic programs, and as such the world is different after they occur. Then people have to work out ways to understand and respond to that new world. Sonny Garcia in Bloomington/Normal Illinois responded by sending out an e-mail to other local activists proposing having a "Conscience-raising" event. (And if you are bothered by his verbal error there please do not become an activist: you would only fuck up the works.) The London riots are now part of the terrain upon which leftists operate. There are no lessons (positive or negative) to learn unless you are planning to start a riot of your own and want to learn how by studying how others have done it.
Carrol