@KnockDownNinjas
The fallacy in your argument is that sites like Pornhub should be entitled to operate as they do, ie, and if there is no practical way of vetting videos before publication, they shouldn't have to.
I think an alternative view is that what they and other similar sites are doing is completely irresponsible. There seems to be the idea that restrictions on self-publication (whether pornographic or not) is unacceptably restrictive in a free society. But this is nonsense. Surely you must realise that until really very recently (until the Internet basically) if you wanted to publish something you went through a publisher, and they took legal responsiblity for what they published. This included the dirty-mac, pencil-moustache, Soho-dwelling publishers the porn mags of old. Society was no less free because of that.
As it happens, I don't have a particularly big deal with that, otherwise I would be a hypocrite for using Mumsnet. However, I do think that certain categories of material ought to be exceptions, and I think porn should be one. Given how intrusive it is, and given the avalanche of videos and images circulated without the subjects' consent, I think this argument is unanswerable.
Just to make my view really clear, I think that banning all porn is unhealthy, as it is a suppression of sexual expression, and the societies that have managed it were ones that were censorious generally (I gave the example of Ireland - Diarmaid Ferriter write an interesting book on this). To my knowledge, the UK never managed it. By "porn" I include, for example, Playboy and I mention this because when porn is discussed I often wonder if such things aren't counted any more as they are so comparatively mild now.
So, my view would be that if Pornhub really was simply used by people as an avenue for their own erotic content, then I wouldn't have a problem with it. However, as a matter of fact it clearly isn't - and I do doubt whether there are many women at all who genuinely don't mind publicising videos of themselves having sex in painful ways.
And if Pornhub and similar sites were closed or blocked, what then? Yes, other sites would come into being, but they could be dealt with. I think that prosecuting people who ran or accessed such sites would probably result in an awful lot of people discovering that actually they don't need to watch extreme porn to get their rocks off. It would result in a huge number of people not being revictimised by having themselves splayed across such sites too. In other words, a win-win. The reality is that, with the exception of a very small number of things, society successfully deals with problematic social issues by criminalising and restricting supply.