I suspect it will happen, sooner or later. I suspect, faced with batons and pepper spray, someone will ratchet up the response, will escalate matters, and from there things will get extremely nasty.
I also strongly suspect that the Occupy leaders, such as they are, are doing their darnedest to keep that from happening, because at that point they will have suffered a tremendous blow. That the movement folks keep speaking out against violent behavior (for normal values of violent) helps, too.
Which, of course, raises the issue of agents provocateurs, whether it's plants in the movement that encourage more violent action, or plants who actually commit violent acts / vandalism and the like (Alternately, there are likely to be some fringe activists who actually think that things should be ratcheted up to the next level; they bear watching for, too.) #ddtb
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Violence for violence « Decrepit Old Fool
Violence for violence. By dof, on November 20th, 2011. In the face of police violence against non-violent protesters, Mike The Mad Biologist asks; Will Occupy Wall Street remain non-violent? “I hope s…

Thomas Jefferson would have approved of the Occupy movement; Gandhi would have approved of its non-violent behavior.
I think most of the Founders would have approved of public action and demonstrations of this sort, at least in theory (some would have been worried about “the mob”). Jefferson would certainly have approved of the mistrust of and anger toward the banks.
Jefferson said a mouthful on the topic–http://www.goodreads.com/quotes/search?commit=Search&page=2&q=thomas+jefferson