I disagree that violence and destruction invalidates any message. The Boston Tea Party is often seen as one of the most important rebellions in United States history, and that involved the destruction of LOTS of property. Any good progress that has been made in the U.S., whether it be women's suffrage, or the Civil Rights Act of 1964, violent riots have been a part of them and have led to a message being heard and laws being implemented. Whether this violence was absolutely necessary for laws to be implemented, that's up for debate but there are definitely some cases in U.S. history in which violence has led to politicians & leaders paying attention to an issue quickly. Not saying this to be inflammatory, and I'm not saying it's a GOOD thing to be violent, because it's not, but to say that violence undermines someone's cause is ignorant of U.S. history of riots and destruction of property being a very effective way of getting a message across.
Also, it's important to remember that on any issue, both sides of the issue (and those in between) are capable of displaying violent actions, and it is silly to reduce only one side to violent actions as I often see in the media. Most of the time one side says the other one is the TRULY violent one, and vice versa, when in reality violence is an issue from any perspective.