I'm also not entirely sure, but isn't stalking a legal offence in the US?

Yes, but they toe the line. One person pulling that shit would be a stalker. But get a whole group of people pulling that shit, and suddenly they're exercising their First Amendment rights of assembly and protest. Also, most places don't have laws that, say, protect your garbage.

I don't think that, in the U.S., there's any legal precedent for issuing a restraining order against a group of people. I would love for a case spawned by this to set that precedent, though. ;)