The specific reason that you cannot yell 'fire' in a crowded theater is that you risk triggering an instinctual panic response that causes people to act irrationally. If we deemed the theater-goers fully responsible for their own actions, we would persecute only the ones who refused to walk towards the exits in an orderly fashion. Various people are suggesting that posting comics of the prophet or making offensive videos is doing the same thing to Muslims: causing a reaction that they cannot control and are therefore not responsible for. I'm not sure I agree. The vast majority of humans panic when they feel threatened in a confined space, so there is a statistical argument to be made for disallowing shouting 'fire' in a crowded venue. The vast majority of Muslims do not become violent when their religion is insulted, so I see no reason to assume that the rioters are not fully culpable for their actions.