According to my father (a World War II veteran who lived in the US) what happened was:
The war raged. The "masses" sat at home and did nothing. There were violent protests in Berkeley, Ann Arbor, and other "radical" places in the mid-sixties. Lyndon Johnson decided not to run. The war raged. The only anti-war discussion among the masses was about the protestors on TV, and how they were traitors. Violent protests continued through the late sixties. There was Woodstock. The average Joe supported the war based on the logic shoved down his throat by newspapers who reprinted the government's spin. He assumed everyone else accepted it, accept the protestors. He continued to discuss the protestors bad actions at work whenever they showed up on TV. They weren't going away.
Slowly, the general public got behind the anti-war movement. It took almost a decade of violent protests before the average USA citizen began peacefully protesting.
Maybe it's a bad example of the success of violent protest. Without the violent protests it's possible the USA would still be in Vietnam and not Iraq. In the USA, the government has learned to use TV "sound-bytes" to counter opposition.
In other countries the masses haven't been quite so programmed. If you read reasons why the USA is hated by much of the world (not just by "extremists"), this reason is at the top of the list.
I think it's quite an accurate example. I would also include the civil rights movement here. With all due respect to Dr Martin Luther King Jr., that with out Malcolm X, the Watts riots, the Black Panther Party, etc african americans would likely still be on the back of the bus. Once again it was the images of violence in the streets and people unafraid to use any means to advance their cause that woke up the sleeping masses.
I am not endorsing violence in terms of physical harm, but to suggest it doesn't work, is never effective, is naive.
And for the record, the violence is being perpetrated everyday against countless numbers of animals. So the idea that violence begets violence... maybe so.. but it didn't start with the AR activists.