These scenes play out the world over. The vast majority of protester are, inevitably, peaceful in almost all events. I say inevitably because human beings are, largely, peaceful except when herded into wars by the masters of this reality.
The psychologists who input to the strategy of the ruling cabal understood many years ago that a few hooded or masked young men (usually fit, square jawed young men on analysis- they even look like police or military) senselessly smashing public property or shop windows, throwing molotov cocktails at the police and starting fights achieves a number of objectives:
First, they deter mass street demonstrations of ordinary people who fear or don't wish to be associated with such acts.
Secondly, they discredit the protesters and by association what they are trying to say.
Thirdly, they escalate the levels of violence and control its direction according to what outcome the rulers desire. This may involve bombs or shootings if the rulers seek chaos, as witnessed everywhere lately, but Libya serves as a pertinent example.
The Greek people must protest their traitorous government, those who have ignored the democratically expressed will of the people and those in opposition groups in Parliament who support the traitors in their crime BUT they should protest with peace and dignity, protesters themselves discovering and filming and pointing out and unmasking and preventing the violent agent provocateurs.
Only in this way will disaster for Greece be avoided.