I do not think that position holds water. If it is just the idea of acting on pedophilia that is wrong, then we need only consider the "lolicon" kink of Japanese manga. There exists a body of manga that appears to hold legal status (or at least no one goes after it) where all you have to say is the character got turned into a vampire when they were a child and are actually 1000 years old, then they can draw them naked for days.

So what then if they stop drawing them with big eyes and small mouths and adopt a more realistic style? At what point do we call the drawing too realistic that it's illegal?

Coming from the other end of the argument, I read once of a legal case where a creeper was taking pictures of local kids walking down the street, printing them out, cutting out their heads, and pasting them on the bodies of nude models. He was deemed not guilty. But was it because it wasn't convincing? What if he had taken the body of a convincingly young model (such as the one case where a man had to fly in a pornstar as a witness in his case to prove she was of legal age after many lay people and doctors swore up and down she was underage...I forget her "name"...Lulu or something). What if he hid the seams but kept the evidence that they were two separate pictures?

Pop this into Photoshop and you can see the case in which scenario A (realistic manga) and scenario B (cut and paste) intersect. Do two demonstrably legal things make something illegal?