I think that, short of civil war, violence against an industrial nation-state is simply not going to affect meaningful change.  The state will virtually always have superior firepower.  Protestors will never win that battle.  Every violent act by protestors will draw an even more violent act from the state.  So to my mind there are two possibilities: either we deliberately involve ourselves in constantly escalating violence, or we acknowledge that, justified or not, it's simply not a battle we can win.

As one poster asked, what are the specific aims that a violent protest aims to achieve?  Let's say that a protestor breaks the windows of a bank.  The end goal of this is what?  The bank is not harmed in any way.  The money to repare that property damage isn't going to come from the CEO's bank account.  If anything, it's going to come in the form of increased service charges to that bank's users.  The bank may even justify the increased service charges as being necessary because of the damage that has been done to them.  That, in turn, sets the bank's customers against the protestors.  But not just the protestors, but their goals as well.   That is a serious problem.

Now, the goal of a peaceful protest, at least in my mind, is not to actually change the behaviour of the state directly.  Rather, it is to raise awareness about the issue and get a broader cross-section of the public to learn about the cause and come on side with it.  This increased mass will, in turn, put increased pressure on politicians to adopt progressive policies.  That's the theory, anyway.  It is quite difficult to tell exactly how well such a thing works.  But it is not at all difficult to say that property destruction is extremely unlikely to get the average citizen on-side; whether activists like it or not, those average citizens are going to have to be part of any successful movement.