Our conclusions:
From a consequentialist perspective, it does not seem justifiable; the balance of consequences seems negative, from the experiences we've learned about. It is possible, however, to claim that the consequences can be positive (think of the US civil war as an example of transformative violence). This needs to be done with great care as it is possible to abuse this argument.
From a contractarian perspective: perhaps we could say that, because there is no viable contract agreed to/upheld by the parties in this discussion, violence could be justifiable, or doesn't have any particular moral content. There are some issues with this: it seems to imply that moral judgments are relative (anything could be in the contract); there is the question of when/if any such contract was explicitly agreed to, or if it is purely hypothetical; and it raises the question of whether there is any morality outside of the bounds of the contract. It leaves open the question of how/why something should be considered moral.
From a Kantian/deontological perspective: our actions, in order to be moral, need to accord with the good will. The decision to use violence would need to respect all of the formulations of the categorical imperative. On the one hand, doesn't violence use people as a means to end? On the other hand, couldn't we add context/details to the formulation of the first CI in order to make it pass the test? For example, details about centuries of historical oppression.
From a care ethics perspective: it dosn't appear to be ethical to use violence, because of the effect that violence has on individual people. On the other hand, it's not permissible to let people harm other people; couldn't it represent a failure to care for people if we don't protect them? That leaves open the question of whether violence is or should be permissible to care for others.
From a virtue ethics perspective: would acting violently be virtuous? It doesn't seem like it; does it fit the golden mean between extremes? On the other hand, maybe it is not fair to demand patience from protestors, and that this doesn't fit the situation well. Looking to moral exemplars might lead us to Gandhi, on the one hand, or to revolutionaries who used violence to achieve social transformation.