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.
I’m with you. I get this is a protest, but I don’t protest gun violence against kids by parading them down a firing range. Taking up the whole road can result in you getting hurt, it doesn’t matter what should be our what your ideals are. It’s a road for cars and behaving like this increases the chance that someone gets hurt.
On top of that this does what every protest that interrupts traffic does, makes people dislike you and your cause.
“I don’t protest racial injustice by going to a segregated lunch counter. That could get you hurt.”
-Lightor, c. 1960.