Home internet would be my guess. Suddenly, kids had access to a whole host of things that *didn't* come with a rating system. Even if it didn't actually change anything about children or their natures, it did give parents something to blame it on. Then you had a few parents who blamed their children's bloody-mindedness and practicality on the internet start censoring things and telling everyone around them what a good parent they are for removing bad material from their children's lives as opposed to actually *teaching them about life* and *explaining* why you don't do certain things. Then it spread.

That said, those giant black tear-shaped things from Charlie and the Great Glass Elevator still freak me out.