I don't think violence will scare the powers-that-be into granting
reforms. Reforms will come ultimately by votes in elections , ballot
initiatives and referenda, that is through peaceful mass action.
Already, Occupy has spurred a campaign for a constitutional amendment
against unlimited corporate money in politics. It has forced economic
inequality into the national political dialogue.
In the short run, the dozens of urban riots in the 60's won some
reforms in the War on Poverty and Great Society. In the long run, it
motivated the Nixon Southern Strategy and the Reaganites, who have
come to dominate the US polity; and they r steadily reversing the 60's
reforms and even the 30's reforms.
I think strict non-violence , which includes peaceful civil
disobedience, should be the Occupy tactic. This will influence mass
voting in our favor.
I don't disagree that the police are the main violent actors in the
Occupation context. Strictly speaking vandalism is not violence,
because violence is force used against humans, not material objects.
However, I think the fundamental problem with BB's and anarchists'
strategy is that it is not to make reforms through voting, so the
tactics are not aimed at influencing votes.