It's a pretty generic 'taking the law in your own hand' argument though. If you illegally double park and as consequence, I illegally shoot you and your whole family, debating what I did is besides the point since the real debate should be about why you double parked.
Ya, it's a ridiculous example but I'm just pointing out the difficulty of codifying vigilantism into law. If illegally killing people who double park is not appropriate, is stealing their TV appropriate? Is hacking their email account appropriate? Who can appropriately be a vigilante? Is it appropriate for a victim who suffered physical injuries? Is it appropriate for a victim who felt offended? Is it appropriate for an eye witness? Is it appropriate for someone who saw it online?
This was a peaceful protest, not vigilante justice. Some people were unable to get to work on time. Where's the outrage about union workers not being able to get to work during a picketed protest?