Earlier quoted context omitted.
I've participated and watched critical mass any number of times. I've never seen cyclists target cars randomly. The only time you will be surrounded in a minivan is if you try to drive through the cyclists, or otherwise act aggressively or unsafely. Critical mass is a protest movement. If you drive your vehicle into the middle of a protest against vehicles in a way that puts people in danger, don't be surprised when…
The situtations I'm describing (covered in the press at the time) were not defensive- they were actively offensive. See https://en.wikipedia.org/wiki/Conflicts_involving_Critical_M... Swarming a car and preventing it from moving- sure, the safest thing for the car to do is stop driving, but... I don't think that's really a good defense of confrontational bikers.
Most of the incidents involving cars were instigated by the drivers of cars. I couldn't find an instance where a car wasn't trying to ride through the cyclists, or the driver hadn't picked a fight verbally.
Can you highlight an incident where cyclists antagonized an otherwise passive observer in a car?