While I've seen the sort of brainwashing you're talking about online, I think in this case there's some justification. The protesters want to make those making racist statements so uncomfortable that they don't want to do it in public. They want to generate a climate that is actively hostile to the idea of "white America" so these sorts of lowlifes crawl back under the rock they came from. It should be shameful to be a white supremacist.
While I don't condone the violence that often accompanies such demonstrations, I think it's important that supremacists meet resistance.