He makes another point that I like a lot: "...when a group of masked white kids break windows in a city that’s many ppl of color, it feels like the white kids are claiming ownership, not saying that this city is all of ours. It makes it harder to build a viable mass movement. I’m saying this knowing the truth, many masked blac bloc folks are NOT white. But, if everyone perceives u as white cuz u have a mask on-then it has the same effect."
He reminds me that the only defenders of Black Bloc tactics I've encountered are white guys like Nick Mamatas. Me, I figure any tactic that makes revolutionaries look like thugs is a stupid tactic.
Do follow the link for more good arguments against Blackblockheads. His point about vanguarding is as strong as any of the rest.