I haven't commented on the Critical Mass incident because I don't have any way of knowing who's version of the story is true. In fact, I find it believable that both groups actually perceived things the way they described. For example, it does seem that both versions seem to include the critical mass riders basically sitting on the drivers car and surrounding the drivers car. The key difference is the Critical Mass riders seem to see that as some non-threatening act of defense to prevent cars from running over other riders. I would argue that is a pretty jacked up view and that it is reasonable for the driver to have felt threatened. If this does in fact happen regularly I am surprised that there haven't been more incidents like this and a CM rider hasn't been killed.
Here's a mental exercise. How would you react if you were riding on the Burke and all of a sudden a big group of walkers surrounded you, grabbed your bike and prevented you from leaving while a massive anti-cycling protest rolled through screaming at you. My guess is most of us would react rather poorly to this.
In general, I am very skeptical of the value of these type of protest groups. I understand that the stated goal is to raise visibility of cyclists rights but I don't really see how creating a hostile environment for people who are no anti-cyclist but drive cars is going to do that. Just because someone drives a car doesn't mean they are the enemy. In fact, we need those people in the cars to support our rights as cyclists. Alienating them seems counter productive to me.
I also question whether the real intent is to promote change or whether Critical Mass isn't just a social group for young people want to belong to the messenger sub-culture.