My concern is that these rides also have the potential to (or actually do) piss off potential allies who could contribute to policy changes that actually make the roads safer and better for cyclists. Any club ride achieves the same goals listed in the Critical Mass website, except they do it without disrupting the lives of automobile commuters.
I am of two minds on this issue. I can certainly see Velocity's point, and when I'm commuting or on a group ride, I try to do everything I can to avoid pissing off drivers, and I encourage other cyclists to do the same.
But then, I also think, who am I to say that a large group of cyclists shouldn't gather and exercise their rights to the road (as long as they act lawfully)? Ultimately, everyone does something to piss somebody off. Tomorrow, I'll be at an anti-war march, an event that I'm sure will inconvenience a lot of people, and may alienate potential allies. Agree or disagree with the war, or cyclists' rights, there is something depressing about a world where people always limit their behavior to avoid inconveniencing others.