There must be a thousand and one ways to achieve their stated objective of protecting children from porn without requiring personal registration for adults. For example, they could implement plans similar to this exclusively for public internet access (for example mobile internet) and then let people install their own porn countermeasures on their residential internet access as they see fit. That way children would be unable to access porn when out and about, and parents could stop them from accessing it when at home. And the rest of us could continue to use porn, at least in our homes, without have to opt in or out or register for anything.
But I suspect this is really just creeping legislation towards the equivalent of a GPS ankle bracelet for the internet, so the government can track individuals wherever they go in cyberspace.