Given how persuasive this argument is, I am a bit surprised that the court was not persuaded. I understand that Ashcroft v. Free Speech Coalition has some distinguishing factors, like the fact that the depictions in question were clearly distinguishable from records of a crime (on account of them not being photographic images of actual minors).
This is a messy and complicated business, it seems like there needs to be a legislative solution since the supreme court can not find what most people consider a just outcome in an interpretation of the statute.