as a semi-local (while i do, in fact, support them) i can say that when a mob of people set out to "shut down the financial district" and wind up fowling up all traffic in the downtown, the cops tend to frown. and to be fair, the cops were fairly well-behaved. you wouldn't know it to look at them, but most of the cops in SF don't really think the war is a smart move, either. a financial district, however, pays their salaries.
From the article, it seems they were doing more than merely dissenting. Y'know, breaking windows, hurling debris, that sort of thing. Illegal stuff, in other words.
However, 1300 is still a fucking huge number, and AFAICT it was "splinter groups" that were doing the real damage. Were *all 1300* vandalising private property? It doesn't seem likely to me -- not *that* many people!