What freaks me out about this is that everything I can think of to mitigate risk I can myself think of a few ways to get around it. The only way I can frame it in my mind is to approach it like an attritional war. Take every step to narrow down the options, then as new ones are exposed work out how to block those.
I'm less concerned with porn users getting their credit card stuff scammed than children inadvertantly or curiously finding their way onto a porn site. In fact in real life we have to cast a weather eye on stds and implicit risks attached to sex, grown adults should be able to assess online risks associated with accessing sexual content too.
I'd agree the government proposal by itself won't solve the problem but I think brainstorming and tossing every available strategy onto the pile is a start.
My only reservation is criminalising parents as hand on heart as tech savvy as I am id be sunk if my kid or a friend of his waltzes out and buys a dongle that connects to mobile network services with a pay as you go sim and accesses illicit content that way. I'm close enough to neighbours houses where their wifi is at or close to full strength so I wouldn't necessarily be able to sniff out a suspicious connection point.
My prediction is the real threat will come from personal devices rather than home internet as I am reasonably confident I can lock down/monitor a home connection, however again what's to stop buying a cheap pay as you go sim and swapping out in a phone/tablet as desired?
I was a cunning little bugger when I was a teen, but I was truly fortunate to grow up just before the internet exploded. Teenage me could probably run rings around parent me! As an adult I have to keep more plates spinning at once than I did as a kid, so I'm going to have to get very cunning again.
I have a few years to get match fit in this, but I empathize immensely with those with fewer tech skills.