I think you're right. My original argument was that when you step inside the mind of someone who does something like this and examine their motives, then you come up with a series of whys. Why are they doing it? Why not just rape/molest the child in private behind closed doors? Clearly there won't be any photographic evidence lying around of their acts in that particular case making the prosecution's case weaker. A part of the reason why they do it because they have a need to perform and every performer needs an audience.
Given how controversial the subject matter is it might seem that I'm making a blanket statement to further my own objectives, but this is more of an observation rather than a conclusion. Why they do it is unclear and up for debate, but the fact that they are doing it isn't. The scenarios you have mentioned did not have this component in them. In those cases the harm is a probabilistic function requiring several requisite conditions to be completed. (someone has to be driving, the speed must be high and so on) A series of things must go wrong and the probability of occurrence isn't 1. On the other hand over here someone must be hurt and I assumed that there must be a psychological feedback mechanism which kicked in for the rapist when people consumed the said matter. That's why I thought it was more reasonable to assert that there is a function of the viewer in the crime itself and that it was a part of the motivations behind the crime.
However what I had forgotten was that correlation does not imply causation and all of this is orthogonal to the actual crime itself. Therefore, I was wrong and you were right. Possession is indeed a victimless crime.
Now we have that fact settled it is indeed an open question where there will be net good or net harm given legalisation or ban. That's a rather difficult question to answer and I do not have the skills or the understanding to broach upon it. However, I think that over here the answer isn't as simple complete legalisation or ban, but rather some X thing in combination with more sophisticated enforcement to catch the perpetrators.
>>> Anders Breivik no doubt enjoyed the media attention and I didn't hear voices calling for his manifesto to become illegal to spread.Again that's a completely orthogonal incident to what is being discussed. The two cases are radically different and have no common ground.