I participated in London, and saw mostly the opposite. Most of the ride was well-behaved and didn't hold people up much, and there were drivers constantly behaving in really dangerous ways, like trying to drive into the mass. Like you and someone else who replied to you, I was uncomfortable with the deliberate blocking of intersections, but "participants should be arrested and charged" is way over the top for what used to happen in London - perhaps SF had a different vibe.