You think there are any city streets in America where people are allowed to walk down the street branding rifles (and in a menacing manner)?
Branding rifles? I think the term you are searching for is brandishing.
So what laws are they breaking? Support your OP that citizens are being terrorized and these guys are violating the law. Watch the video YOU posted. No threatening behavior unless you feel anyone owning a firearm constitutes a threat. (I see you're from California so a safe assumption).
You're still defying what the police department clearly implied; that they are not legally allowed to be brandishing those firearms. I think you're the one that needs support if that's indeed what you're attempting to do.
And the dress and demeanor of the armed participants as well as holding an illegal tribunal is clearly meant to intimidate and harass society. This is clear to any reasonable observer.