I'm now pretty convinced that this is the best argument for persuading non-technical and non-internet-privacy minded people why this is a problem. It's hard to explain all the technical factors that make it impossible to implement without compromising privacy... but it's pretty easy to get them to understand the real intent. If you start them thinking through what mechanisms would make sense _if_ the original premise truly was protecting kids from content they aren't ready to see, it's easy to arrive at that answer, and equally easy to see why "everyone must provide their ID so we can verify their age" probably comes from other motivations.