At last, something that could potentially challenge Facebook's world domination. Somebody gets a federated social network running with a substantial user base, and it runs into this.

The US position on child pornography comes from the Meese Report during the Reagan administration.[1] The Reagan administration wanted to crack down on pornography in general to cater to the religious base. But they'd run into First Amendment problems and the courts wouldn't go along. So child pornography, which barely existed at the time, was made the justification for a crackdown. By creating ambiguous laws with severe penalties for child pornography and complex recordkeeping requirements, the plan was to make it too dangerous for adult pornography to be made commercially. But the industry adapted, filling out and filing the "2257 paperwork" as required.[2] After much litigation, things settled down, porn producers kept the required records, and DoJ stopped hassling them about this.

So that's how the US got here. That's why it's such a big deal legally in the US, rather than being a branch of child labor law. Japan doesn't have the same political history.

Federated systems are stuck with the basic problem of distributed online social systems: anonymity plus wide distribution empowers assholes. That's why Facebook has a "real name" policy - it keeps the jerk level down.

[1] https://babel.hathitrust.org/cgi/pt?id=mdp.39015058809065;vi... [2] https://en.wikipedia.org/wiki/Child_Protection_and_Obscenity...