The purpose is ostensibly to prevent underage people from "illegally" seeing porn. You don't think teenagers would seek out "porn-enabled" computers? "Computer

The purpose is ostensibly to prevent underage people from "illegally" seeing porn. You don't think teenagers would seek out "porn-enabled" computers? "Computer == identity" is simply broken. (It's also broken the other way - there's absolutely no reason to charge per-device merely to authenticate age.)