The incentivizing argument seems to be a red herring because in no universe would we legalize some subset of child porn that is shown to not incentivize more being produced, no matter how clearly such a case was shown.
Drawn and computer generated images of that kind are legal under the First Amendment in the USA. I mention it because they are, in contrast, illegal in Canada.
The other argument is that it inflames and encourages desire to assault children in a significant subset (in the sense of risk; i.e. the population doesn't have to be large, only the risk) of those who consume it, and that it does so in a unique way, compared to other forms of media. The other argument is that it's a particularly grave violation of the child's privacy, one they cannot consent to.
Alternatively, we could just bite the bullet and conclude (perhaps rightly) that maybe porn in general has the same negative effects we allege CP to have. I'm not sure if that's true, but if it is, then I think it would make a good case for banning it.
