> it would enforce optional controls for the bill payer,

They do; in the UK, if you want to have access to porn, you need to tell your ISP and they will unblock it.

Of course, that's a game of whack-a-mole because you can render porn in Minecraft servers or join one of many communities on Whatsapp or Discord if needs be. It mainly blocks the well-known bigger porn sites.

In which case there is no need for anything else.