There has to be a balance. I've never had a problem with Critical Mass before and know that in general they are regarded fondly in London.
However the fact that there were four times the amount of cyclists and that it ended in arrest, whereas, I don't recall that happening before, suggests to me that you had people joining with a different agenda than usual - to make trouble. You know the sort - the type of people with no interest in any interest in positive change, just in starting fight so they can brag about it afterwards. About police "brutality" because, apparently, they are free to assault whoever they so desire but if anyone so much as tuts at them, it's a human rights infraction.
People, usually, who have such a privilleged and easy life, they have nothing really to protest about.
Let's call them Trustafarians.