This is the kind of mind-bending argument twists that Ciro Santilli loves. If we take out the "a real child is hurt" aspect, does it still make sense to make it illegal?
Of course, hentai of young-looking girls has already existed since forever. Bit with newer image generation methods in the 2020s used for computer generated child pornography, especially sometimes photorealistic text-to-image generation, things are taken to another level.