I think they've always been there. They've just been quiet about it, because they've been relatively isolated. The internet has allowed them to find each other, form stronger communities, and coordinate their actions (of which upvote/downvote brigades on sites like this one are the least of our worries BTW), making the whole much more potent than the sum of its parts. As I said, this same ease of communication is wonderful when it's all in a good cause, but it can also be used in a bad one.