Can Unpeaceful Protest Ever Be Justifiable?

See this letter below (found on facebook, so sorry I have no reference):It's not exactly what I would have said, but overall clarifies a very good point.So some Californian 'film maker' made an offensive video with the hope of getting a rise out of the Islamic community? And you react to your disgust with riots and violence? This isn't 'an eye for an eye', this is unpeaceful protest and it is totally unjustifiable.
Fair enough, you've been offended, take legal action, get the bastards who pissed on your beliefs. Don't attack every non-Muslim in the world simply for being non-Muslim! It gives Islam a bad name, Islam doesn't condone violence, so who does condone this?This isn't a reasonable response and only opens up room for more insults and negative judgment.