It is important to remember that child pornography is evidence of a crime. People do not send that evidence to others without receiving compensation of some sort; the knowledge that others are looking at the images is knowledge that they have evidence of the crime. The people who commit crimes against children are very secretive, and those who produce child pornography often go to great lengths to remain undetected. It is clear from what is known about online child pornography exchanges that trade of some kind is occurring, often serving a dual-role of compensation and of filtering out law enforcement officers.
That is the real issue: these people know that once their photos and videos spread around, the police will become aware of them. Rather than knowing that people enjoy their work, what the producers of child pornography know is that their work can lead to their arrest. They are exchanging it because they are receiving enough in return to justify such risks.
The original legal justification for the censorship of child pornography was to remove that compensation, since the police were having so much trouble locating child pornography producers. My point is that that justification is now badly in need of review, because the majority of people guilty of child pornography possession did not compensate the producers in any way. I have no problem with raids on forums where child pornography is exchanged quid pro quo; my problem is with raids on people suspected of downloading child pornography from peer to peer networks or third/fourth/fifth/etc. hand websites that are many levels removed from the producers. At the very least, prosecutors should be required to show that the imagery was paid for in some way, whether by barter or with money.
That was the dubious argument made decades ago, when the only way to obtain pornography of any kind was to purchase it. In today's world, it is far more common for people to download child pornography without ever having paid for it. People are arrested for downloading such videos from peer to peer file sharing networks all the time, almost always without any evidence that they paid for it, knew who made it, or were in any way encouraging its production. Just having child pornography in your browser cache is sufficient to be charged in New York.
It is clear at this point that the purpose of child pornography law is not to protect children, but to punish adults regardless of whether children are involved. It is illegal to possess cartoon depictions of child pornography, even if you possess no other imagery:
http://io9.com/5272107/manga-collection-ruled-child-pornogra...
http://www.comicsalliance.com/2011/06/27/u-s-citizen-arreste...
Like most laws that increase police power, this has gotten completely out of control and put the public in danger.