I don't think anyone's too worried about a teenager having a cheeky look, you're simply not going to stop them. It's more about preventing primary school aged kids seeing it. That and making it a little more difficult for younger teenagers.
There's two sep discussions from that really:
Should they be able to see that sort of content or not?
If no, how do you go about it blocking it?
I definitely think it's unhealthy for young children to see that kind of content (I think for some adults it's probably unhealthy too). Have friends who are primary (and secondary) school teachers and some of the things they overhear the boys talking about as though it was normal sexual behaviour... you'd never let your daughter out again. But I don't think blocking it outright is a cureall since education must play a part in it as you can't let the idea that some of this stuff is 'normal'.
I think porn in excess, even for adults, can be pretty unhealthy when it starts to become a substitute for real, meaningful, contact with the opposite sex. That goes for those in and out of relationships.
Saying there's no point blocking it as there's so much out there sounds a bit like the argument the pro gun ownership folks make when talking about gun control in the US. Not a great argument imo.
No way should anyone be made to sign into a pornsite with their credit card info though - that's just mental. Depending on how they implement this it won't drive porn into the underground though. Why would it? These steps are to stop kids looking at it, not adults.
Couple other points - 90% of parents barely know how to setup a password on their pcs, let alone setup child block filters.
90% or young kids won't have a clue how to setup a vpn or even what one is.
I've totally made up the above two %s. Sue me.