Yeah, power can be abused, what else is new? But people joining for a cause also doesn't do much if they don't have the means to enforce their cause with violence - usually they'll just get overwhelmed by whoever does have the means for violence. Peaceful revolutions are possible (e.g. Indian independence), but they require relatively specific circumstances and a lot of people who are willing to stay nonviolent even as they're beaten up (and worse) by the police. I suppose you can do almost anything peacefully if your group is large enough and has enough cohesion, but that's incredibly difficult to achieve and I think it's actually more difficult nowadays, because everyone has a handheld communication device on them at all times that's filled with fascist propaganda.