It obviously depends on the context. I really don't understand this modern tendency to have very strong a-priori stances on what forms of protest are good or bad. Obviously physical violence is beyond the pale in the context of a functioning democracy, but beyond that, I don't know why we should categorically endorse or condemn a particular form of political advocacy without considering the wheres, whens, hows and whys of it.
I agree when it comes to this particular form of protest, but I think there are definitely other forms of protest that we can categorically dismiss as stupid. Blocking traffic, for example, is extremely selfish and dangerous-- plus it has the added bonus of p*ssing off everyone you're trying to win over.