It's worth mentioning that in this instance the guy did send porn to a minor. This isn't exactly a cut and dry, "guy used stable diffusion wrong" case. He was distributing it and grooming a kid.
The major concern to me, is that there isn't really any guidance from the FBI on what you can and can't do, which may lead to some big issues.
For example, websites like novelai make a business out of providing pornographic, anime-style image generation. The models they use deliberately tuned to provide abstract, "artistic" styles, but they can generate semi realistic images.
Now, let's say a criminal group uses novelai to produce CSAM of real people via the inpainting tools. Let's say the FBI cast a wide net and begins surveillance of novelai's userbase.
Is every person who goes on there and types, "Loli" or "Anya from spy x family, realistic, NSFW" (that's an underaged character) going to get a letter in the mail from the FBI? I feel like it's within the realm of possibility. What about "teen girls gone wild, NSFW?" Or "young man, no facial body hair, naked, NSFW?"
This is NOT a good scenario, imo. The systems used to produce harmful images being the same systems used to produce benign or borderline images. It's a dangerous mix, and throws the whole enterprise into question.