Now, more than ever, Critical Mass rides are a positive thing for Edmonton. The police are cracking down on bicycles on the sidewalk. Many people are afraid to ride on the road so they won't ride at all. Critical Mass rides give people enough confidence assert a portion of the road to themselves to ride on and to resist bullying. The rides here only take up one lane as was requested by the police. We're proving that you don't have to race at a 30kph pace in order to not get run down on the road. It's not so much a "one less car" movement as it is a "one less terrified cyclist" movement. It's like swimming with a school of fish.
I can't speak for other cities because people and the authorities are extremely different in other cities. As far as Edmonton goes, Critical Mass works without touble with the police.