That's a really good question -- the short answer is it's a really great motivator. Some random pedophile, who wants to obtain child porn, first must learn how, and in the process they would have to learn some basic computer skills, as well as learning to bypass the mechanisms we (rightly) have in place to prevent such material from being distributed, and to catch those who download it. This is why malcontent teenagers who would want to do something like DDoS tumblr are far more likely to know how to do that than well-adjusted teenagers who don't care.