The point of criminalizing the data is to suppress the market for it in order to reduce the incentives to create it.
"Suppressing" the market is impossible. How did it work with drugs? or with alcohol?
The law of the unintended consequences strikes again.
For alcohol, consumption shortly after Prohibition in the US fell to about 30% of pre-Prohibition levels. It then increased over the next few years to about 60-70% of pre-Prohibition levels. It stayed at that level until Prohibition was repealed, and stayed there for a bit after then climbed over the next decade back to pre-Prohibition levels. Cite: Alcohol Consumption During Prohibition, Jeffrey A. Miron and Jeffrey Zwiebel, The American Economic Review, Vol. 81, No. 2 (May, 1991), pp. 242-247.
Yes, it is awkward to compare something as awful with something as intangible as anonymity. But if you don't draw the line somewhere you will not be able to have a functional society - in which case we might as well be as humane as humanly possible and make good use of our nukes and make sure that there will be no human suffering in the future to worry about.
I'm more worried about all the people abusing children without doing us the courtesy of publicizing the fact on the Internet.
think of it like this: it is legal to posses or make video footage of a murder. but it is still illegal to kill someone for the purpose of making such a film.