Age verification itself isn't such a bad thing. I feel most people are more angry about having to verify their actual identity. Every ad provider knows your address and complete identity every time you log into anything though. I guess its the illusion of anonymity that's so popular.
Horseshit.
There's often a degree of uncertainty with the data advertisers have. This would heavily reduce that uncertainty and enable worse behavior on the part of advertisers.
Age verification is an excuse for identity checking.