Black bloc (bb) gives the police the perfect alibi and you have to be willfully ignorant not to see this. That single teacher who just got arrested for voicing her opposition to the superintendent's raise did more to the American left in a single day than bb did over two decades (which, I'd argue is actually negative).
The popular image that "the left has no program, they resort to vandalism" is reinforced by deeply flawed and ideological tactics as bb, but even worse, the participants of bb think of themselves as brave radicals while in fact they are just performing meaningless acting outs and nihilistic fanaticism against… against what? Advocates of bb would say "against the state," but infrastructure is actually the thing we need regardless who provided it, smashing shop windows is the private sector not the state (and hardly an attack on capitalism as such), while playing cat and mouse games with the police is completely normalized by now: riot porn is pure spectacle, not an inch more than live car chases on TV.
This all boils down to the idiotic conceptions of what radicals should do like propaganda of the deed and other similarly babby-tier theories. You burning down a street has no inherent (let alone radical) message, your acts don't speak for themselves, they are interpreted, in fact, you opt for meaningless violence exactly because you can't speak for yourself.
But this is their game, you moron. Your shit (a)politics is the norm, spectacular/aesthetic activism is the mainstream, meaningless violence is the language shared by ISIS, bb, random outbursts of shooters. The old ideas about the liberatory potential of terrorism lost their edge long ago – and bb isn't even proper terrorism, ffs, it's just a carnival for kids who have no theory or proper tactics.
BB was the final nail in the coffin of OWS. First the horizontalist principles of OWS denied forming a cohesive front, program, media appearance, while establishing a group of "totally not leader" leaders, then the movement crapped its pants over the beautiful meaninglessness of the multiplicities of opinions, so finally bb could end it all in flames much to the dislike of many participants.
To think that those who oppose bb are pacifist is fucking laughable. I'd go as far as to say that it is bb which is pacifist, its pseudo-activism ensures that the things can go on as they do. Nothing is more relaxing for a politician to see that his opposition consists of kids crashing store windows, the point at which the politician starts to shit his pants in fear when he sees a growing mass movement of hundreds of thousands unified under a revolutionary program with competent and dedicated leadership and disciplined manner.