They are the exact leftist equivalent of the right-wingnuts who claim that the goverment is run by Zionists, Federal Reserve notes aren't legal currency, the government is building secret mass detention camps, the NAFTA highway will be used to ferry Chinese troops from Central America to Des Moines, etc, etc.
And remember everyone thought those types were reasonably harmless until one of them parked a rental van in front of a Federal building in Oklahoma City.
These "citizen arrests for war criminals" types worry me just as much as the extremist anti-government right-wingnuts. Eventually one of these lefties will go Timothy McVeigh. It's just a matter of time.
I am often concerned for the safety of many conservative folks whether in office or otherwise. As you are saying it could ignite on a huge scale.
I have seen many of these type of protesters at specific events and also in the streets of Seattle during WTO back in 1999 and I too am very surprised nothing more has happened. There is this sort of walking, possessed dead look and mannerism in many of these types and the aggression level goes without saying--over the top.
Paultards!