Just thought I'd throw that out there.
I'd draw a distinction between the two... in many cities graffiti artwork can be quite valuable and beautiful (and political). Some cities even fund graffiti artists to do public murals in approved spaces.
Also there's gradations of oppression, too.
If we were living in a complete police state (like Syria) I don't think most people who favored peaceful resistance would complain if someone spray-painted "freedom" on the police station.
But we're in an awkward situation of living in a declining superpower with extensive traditions of democracy that are only nominally enforced at this point. Like the late Roman republic. This means that we're in a position where the vast majority of the 99% has a deep seated patriotic desire to see ourselves as a fundamentally sound nation where the system isn't broke and spray-painting slogans and smashing windows only serves to damage what ain't broke.
What saddens me about the psychology of vandalism is that people vandalize small proprietors' windows all the time for non-political reasons and they get no help or sympathy from the community, only "I hope you have insurance." So smashing windos is ultimately a useless gesture that only serves to anger people who object to vandalism when it is done out of hate, but are unconcerned when it is done out of simple theft.
I think that's the real concern here. Is it an action that is being done out of hate? Or is it the only way to stop something from happening? I'd have no objection if somepony smashed a lock to occupy a premises to prevent a house from being foreclosed on, or a building torn down to make way for a Wal-mart. Sadly, the right wing vandalizes "unwanted" stores all the time out of hate, and it rarely gets reported on because in hate crime, it's the businesses that have no power in the community. If it's a mob violence then I'd put it in that category.
In any case, anyone looking to monkeywrench, say, a Wal-mart should not do so under the Occupy flag, as it's against the organizing practices of Occupy to engage in vandalism in general.
Let's not forget the idea is to Occupy public space and improve it (i.e. better it) by creating an island of public democracy where people can participate directly in resistance ansd/or change.