I should say that a protest is implicitly a threat of violence. The purpose of protest is to physically manifest a representation of the number of people angry about a thing, with the intent of planting the idea in the minds of the audience "There are enough people angry about [thing] to cause real destruction if they turn violent. Do not provoke them."

That threat, however, only rings true if there are not recreational protestors, unwilling to suffer injury for their participation. The recent policies of non-intervention in protest-concurrent looting and casual property damage have decreased somewhat the value of protests, because the audience understands that a significant percentage of participants are actually just there for a new pair of Jordans.