If they have serious mental issues, then by all the gods, they should NOT have been reading creepypasta. That scares adults, ffs. It only reinforces what I said, that parents have an obligation to make sure they know where their children are surfing on the Internet. And a large part of what's wrong with the Internet generation is that there is NO concept of consequences. No one expects them to take responsibility for their actions. No one wants to say, "You screwed up, and you are going to receive a punishment." I knew that if I screwed up, I was going to get spanked, lose privileges, and be generally miserable until I'd been deemed sufficiently punished. Guess what? I grew up to be a fairly good person, who gets involved with the community, obeys the law, works hard, pays taxes, and doesn't litter.
I've raised two children. I have one who's 19 and one who's 16, and I monitored their Internet usage. They earned privileges based on both age and how well they obeyed the restrictions I'd imposed on where they could surf. Neither one of them has ever shown any inclination to lure classmates into the woods and stab them to prove to a fictional character that they were "worthy." And if they ever had entertained such gruesome notions, I'd have known about it long before it got past the "what if we..." stage. I understood that kids don't spring into the world with a font of altruism waiting to be unleashed. They're largely amoral, selfish, impatient, and not at all empathetic. It's up to parents to instill some sort of values in their children. I'm not playing with theory here. I've lived it, and I'm speaking from experience.
It's not rocket science, people. It's called parenting. It's what OUR parents did, and it works.