Look at the London riots, nothing was achieved because they protested the wrong way :[
Those were flat out riots, not protests.
There was no unifying reason to hit the streets, no goals or objectives, no coordination or attempts at coordination. It was people stealing things and trashing businesses.
Some people tried to assign political purpose to their actions, but that was a stupid attempt at opportunism and simply hurt their causes.
Worse, it hurt the causes of people trying to explain or understand the riots in political terms as they were painted as trying to excuse such behaviour.
The danger with these protests is that they can go the same way. Or be dragged that way
If there was a group that decided - for clear political reasons and with definite goals - to break the law, that would be fine with me. Similarly if a general protest crosses the line occasionally in terms of legality, that's fine, so long as the crimes are justifiable in terms of the protest (eg, illegally occupying a space).
When a protest is used to cover illegal behaviour just for shits and giggles, I have problems. And so does the group and movement behind that protest.
In Oakland it looks like the police have messed up badly. The mix of groups reported, both before and after the crack down, would likely have self destructed and possibly harmed the wider movement. The violent police reaction both gave extra cover to the more violent protesters and galvanised the peaceful groups.