I honestly don't understand why people are calling it a nanny state issue. Porn is illegal for under 18's to purchase, but they can consume it on the Internet with no age checks etc. Before the internet kids couldnt just walk into a shop and buy this stuff. Just because it's online doesn't make a difference. If kids as young as ten were able to order cigarettes online people would be in uproar, same with alcohol.
Now I get that this, in part, is down to education from the parents, but kids are still curious and they will still look/find a way to look.
And let's remember the sheer amount of very hardcore stuff that is so readily available it barely needs searching for. For young people who haven't embarked on any real life sexual experiences, this will shape what they think is normal/acceptable. I have very personal experience on this.
I believe that if you were to ask teenagers about what is expected of them once they become sexually active you'd be shocked at their answers. The problem isn't solely boys (and I wouldn't suggest that for a minute) but asking boys "would you expect a girl to do x,y,z or feel its acceptable to ask a girl to do x,y,z when you first start seeing each other" they would think that an awful lot of things that should be reserved for those in trusting, long term, well established relationships is perfectly acceptable to not only request but expect with someone their own age.
This combined with a culture of boys will be boys (an attitude that both encourages teen porn consumption, and also means that boys sexual "conquests" are celebrated) means that some girls feel like they have to say yes to these things. That these things are normal and if they say no then they're "stiff", "frigid" or a "prude".
Porn also teaches the less experienced viewer that sex is purely for self gratification. And I think there's a lot of people who have experienced this as a problem.
I once went out with someone who had an extensive stash of fairly hardcore porn he'd managed to swipe off his older brother (was in the days of the Internet but before it was so readily available, so no Internet consumption here) and during one of our first sexual encounters he asked if he could cum on my face. We were both 16. He was otherwise very caring and sweet. I'm not prepared to go into more details of my personal experiences but you get the idea.
He got the idea for that through porn and the more he saw the more he believed that was a normal way to behave. Now, if he'd been 18 when he first saw all of those things he would have had some sexual experience behind him. He'd have known what real sex with a real person was like and would have been able to saparate what is a fantasy from what is a reality. He would have realised that sex isn't about personal gratification but mutual gratification. I wouldn't have been treated like like more than an object. As I said, otherwise he was a perfectly decent, very caring guy. He just honestly thought this was all normal. And he can't be the only to have been affected in this way.
And remember, that was all with magazines, not the copious extreme stuff that's so readily available online. And the thing is, it's not a blanket ban-you can opt in if you like and that's fine. But something needs to be done about what our teenagers have access to and this is one way of doing that. Education is also key and I'll be teaching my DD and DC2 how to be respectful etc etc and monitoring Internet usage. But we all have Internet on our phones now and it's hard to monitor.