And the only reason it is permissible to presumptively treat people as underage until proven otherwise in the physical world is that there isn't a constellation of intermediaries collecting all your habits and preferences when you buy porno magazines or alcohol in person.
Why is the answer people seem to arrive at being "mandatory collection of blackmail material that will ruin careers and relationships" when it comes to the Internet?
Because "somebody has to think of the children." At this point, I am convinced parental instincts are being abused to slowly but surely install more-or-less complete public surveilance. Its a rather obvious approach. You have to appeal to something emotional. And parents, and their apparent unwillingness to take up responsibility for their parenting, are the perfect target. Even child-less adults will chime in to toot the "Somebody has to think of the children" mantra.