I entirely disagree that specific, individual violence / serious damage to property can be justified / defended on the basis of generalised, non-violent things that may have happened. This may help
explain why it done, it may be
mitigation for what is done ... but it is not the police's role (nor should it be) to stand by and go "Oh, OK mate, yeah you've got a point - those bankers bonuses are a bit obscene, crack on and beat that random bank-related cunt to a pulp and set fire to the building. I'll hold your coat if you like ..."