User blog comment:Gundam Legilis/The Fallacy of The White Fang/@comment-4010415-20140421160145

I figure the transition happened via one or more members of the White Fang speaking out that "None of this is working" and "They will never respect us. All they do is treat us like garbage." Maybe they did a little demonstration at some point. I think after the first violent act worked, other faunus took notice and started to listen more, realizing "Maybe he's right. Our peaceful protests and attempts at negotiation weren't working, but this... this actually worked."

As for whoever started the change to a more violent attitude, all I can say is that I assume he just snapped. It's hard to explain it. When I was a kid, I was being bullied, and I just stood there and tried to ignore them, thinking that being passive and peaceful would get them to stop. It didn't. One day, though, I snapped and started attacking my bullies. Eventually, it got to the point where they left me alone 99% of the time. It was several years before I dropped the "Violence is the solution to all problems" attitude.

TL;DR: After being treated like dirt and kicked while you're down for a long enough time, having a taste of violence getting you what you want can make you decide to start using violence more often.