Can you show examples? This is feeling like a hypothetical you're using to dismiss political speech rather than a genuine concern. I don't doubt it's happened (I can think of a couple of anecdotal examples I've seen in person, as well as plenty of times we let cops through even though we were fully against them), but I also don't think you may have a respect for just how many peaceful protests block roads or buildings in this country every single day without major incidents. As someone else pointed out in this topic: the revolution isn't televised.
I appreciate (really, a lot) that you've been commenting civilly. But HN isn't a forum to be used primarily for political or ideological battle. It is for stories and conversations that gratify intellectual curiosity. Those things don't sit well together, because the more powerful forces (political battle) eventually overwhelm the more delicate ones (intellectual curiosity).
