Great piece. A must read. Those people threatening fellow protesters were not anarchists! Those were agents of the state masquerading as anarchists. No anarchist worth his balaclava would do anything to undermine an uprising like this. Clearly this was the state sending their people out amongst the protesters to sow division, and commit acts of destruction which would give the authorities the pretext to disperse, arrest etc.
A note on the Back Bloc: It is a technique, not a political faction. It is simply a mass event in which a direct action is taken. Participants cover themselves to hide their identities from the public and from one another. This makes the practice subject to easy police infiltration. I have never engaged in such action, so it is hard for me to judge, but my guess is that the vast majority of these events are organized by the police, and most of the participants in them are cops. They have been caught several times (as no doubt occurred in the instance described in the article) and police have had to testify in courts in N. America and Europe that it was they who instigated violence in the guise of Black Bloc and/or anarchists.