This was a Critical Mass event, which is why the bicyclists are taking up all of the street as a way to reclaim the streets and protest the lack of safety for riders under usual conditions. It’s not legal, but protests are never useful if they’re fully legal now, are they.
There is a freekonomic episode about how the easiest way to murder someone in US is to run them with your car. There is a reasonable chance you’ll go free. US is so car-centric that it’s a dogma that car accidents are unavoidable part of life.
So “for bike lane” seams very reductive.
There is an argument that more people will die because lack of protest like that than during those.
This hypothetically raging lunatic don’t disappear when you are alone, trying to survive on the infrastructure build without any consideration that you exist. If he’s a danger here, he’s a danger there. Where you are alone.
(Also, where I live protest like those are coordinated with police. Why is no one protecting nor serving here?)