A couple of points to consider.
People have done horrible things and then turned to free speech and right not to incriminate oneself and such and gotten away with it. People have done horrible things and gotten off on a technicality or because the AG/CPS/... fscked up the paperwork. Why prevention of getting away with it for a bad few suddenly should cost everybody's fundamental freedoms* just because it somehow involves the internet, the 'web, cyberspaaace, seems to me a little hard to argue. By all means, try and convince me. Haven't seen a politician successfully do it so far, though plenty of them assume there's a difference somehow.
Personally I think the only thing worthwhile to pursue in child pornography** is the sexually abusing of children. That happens, surprise surprise, in the real world. Often this involves close family friends, relatives, even the children's own parents.
No reason to blame "teh intarwebs" as the hideout of the bad grownups. That the discussion centers on this proxy means we're not willing to face the bugbear and in doing so risk sacrificing valuable things without return for anyone, least of all the children.
The main thing I would point out here is that if we'd pick the abuse, instead of the pictures, to go after, we'd squarely have to find the perps in the real world, even if there's clues to be found on the 'net. It also would simplify questions of jurisdiction quite a lot. Apparently that sort of focus is not in the interest of groups like the IWF.
I'm not too worried about the abuse of anonymity, by the by. Looking back at how I grew up on electronic message exchange systems (predating internet) I mouthed off quite a lot in very poor language and under what amounts to my real name. Here, I've posted almost two days worth of commentarding, all anonymously, and it's generally been quite civil. Being anonymous at home mouthing off to all the world is seductive but also something most of us get over at some point.
Give it a few generations and the situation will change. Maybe someday even most parents will understand that you don't let children participate in places where you need quite thick skin to avoid getting hurt, and instead they'll take their own responsibility in supervising their offspring on the 'net instead of demanding someone else makes the bad bullies go away. The main thing is that we have barely a generation worth of people that grew up with all this power to vent our spleen, get in flame wars, and so on, and so forth. The 'net is full of dark places. No need to try and turn all of it into teletubbieland.
Also note that concluding to have to abolish all anonymity is of course a little silly. Take again the real world. How realistic would it be to demand that everyone must always leave their calling wherever they've been, because otherwise catching, say, burglars or muggers or rapists would be Just Too Hard for the police?***
Of course we could build computer systems that track your every move, always. And of course power mad politicians would absolutely love exactly that. Until perhaps they realise what they've done, but then it might be too late or just horribly painful to rid us of the monster of total control again.
But now that we can, we have to ask ourselves, do we really want to do that? Or should we build systems that instead preserve anonymity? Even at the cost of making it less easy for police inspectors to be lazy? Looking at how we hobble the police in the real world just to make sure they don't get too nosy, that ought to be a no-brainer. Then why isn't it?
* Provided we did assign everybody those. It's a cultural thing, no matter what the UN professes. Not that I don't like those things, mind. Just that the "universality" is more often claimed than that it actually has substance. Do note that I am only pointing out this is a whole 'nother can'o'worms, nothing else. But I digress.
** Implicitly restricting the discussion to involvement of pre-pubescent, real, children because otherwise age of consent, which isn't universal by a long shot. Portugal has it at 14, I believe. Everybody else are just prudes. Yeah, that's it. And 'real' children because otherwise the extreme pr0n law kicks in. Anyhow, yet another can'o'worms. Best not go there either.
*** Effectively this already happens in some places, like how over in the Netherlands a certain controversial political party demands every visitor's state identification number (BSN, like SSN but actually unique and already subject to official feature creep; still this wasn't what it was ment for and thus, strictly speaking, shouldn't be allowed) and this was defended with the claim that otherwise the national police security service wouldn't be able to check on them. Yes, official claim. No wonder pc plod can't catch a thief.