I've never been around an activist group that didn't turn into an endless series of petty purity tests. I was raised in a church where everyone was looking for more and more inconsequential things to judge each other by.. The natural evolution is toward tighter and tighter criteria for what behavior gets you shunned from the group. The end result is that the central cause can be as pure as the driven snow, and yet the tone will get more and more toxic over time, the members becoming less and less charitable with each other.
You hear experts talk about how extremists get "radicalized." But it really isn't a mystery, and we all form less-murderous versions of this. All it takes is a closed like-minded social circle in which it's considered unacceptable to disagree with the group, and then devote that group to hating something. It doesn't even matter if the thing truly deserves hating -- it still turns toxic. In fact, it works better if it does. "How can you criticize any flaw in our group's behavior when the other side is Nazis! That's literally saying that both sides are the same! The mere existence of pure evil on the other side mathematically means our side is pure good!"
At that point, no criticism is possible and there is nothing to moderate the rage. The rhetoric ratchets higher and higher as each member tries to top each other (to prove their own righteousness by demonstrating they hate the target most), and there is no method for reining it in. Anyone from the inside who takes a moderate tone can be shouted down with accusations of being an enemy sympathizer.
Living purely in opposition to something, rather than for something, hollows you out inside. To be a whole human being, you have to spend your life building something good.
David Wong writing for Cracked