Online ‘Pedophile Hunters’ Are Growing More Violent — and Going Viral: With the rise of loosely moderated social media platforms, a fringe vigilante movement is experiencing a dangerous evolution.
I’d make a guess they’re getting violent because the legal system can’t do anything with their compromised evidence. Instead of realizing they’re not the people qualified to do this work, they’re just doubling down and “handling it themselves.”
They're experiencing positive re-enforcement when they get violent with the people they've intrapped. They're getting more violent because they want more of the positive online feedback they've been getting.
I don't know how it works in the US, and it's certainly not perfect, but if you bring "compromised" evidences of actual child abuse, you can be sure it'll trigger some extensive investigation. Sometimes, this leads to nothing. Sometimes, the "evidences" were not really evidence, but more of a hunch. Sometimes, it leads to actual consequences.
One issue with such a vigilante system is that sometimes, you're wrong. That's why due process is a thing. But the "this evidence was collected illegally, so we won't even look up the guy" thing isn't really a thing, as long as the evidence is better than "I'm sure of it".