Why do you keep repeating the claim that people involved in Black Blocs think that they are a 'spectacle' which will immediately 'bring down capitalism'? Chuck has already pointed out a number of Black Bloc communiques in which they show quite different motivations.
Black Bloc actions are one tactic among many, adopted not with a view to communication or the creation of 'spectacle', but because of the concrete effects it has on participants. No-one thinks Black Blocs alone will bring down capitalism, but they do have a particular value in anti-capitalist struggle.
As Alain Badiou argues, part of the power of the capitalist state lies in its imeasurability: because of capitalism's centrality to all our lives, it presents itself as being not simply powerful but unchallengeable. Self-organised militant opposition to capitalism, even if in the attenuated and symbolic form of smashing MacDonald's windows, forces the capitalist state to become measurable (crudely - to send cops after you), and that is itself an important ideological victory.
Of course, this isn't a substitute for community organising or workplace struggle - but no-one thinks it is (except uninformed liberal and leftist critics of Black Blocs). On the contrary, people involved in Black Blocs can take the experience of self-organising, and the self-confidence that comes from confronting and perhaps briefly defeating the state, and use that in their other work.
I'd also point out that this seems to be a curiously insular North American debate - in Europe, pretty much every protest involves the destruction of every ATM along its route, for example; and yet the anarchist movement in Europe has strong community roots and continues to grow.
-- Etienne <tim_boetie at fastmail.fm> http://huh.34sp.com/