In my mind, the difference is in the legality of the material, and the degree to which said material can be effectively simulated. Due to the illegal nature of the material, and the limited number of people who are interested in it, there is not a developed profession of experts in simulating child abuse. As such, the majority of images of child abuse are created by actually abusing children. Combine that with offenders use of trading mechanisms, and the the desire for "new" images, it's easy to see how demand for images of child abuse increases the number of children being abused.
On the other hand, violence is not illegal to depict, and there are many professionals who are experts in simulating violence without actually causing harm. This results in violence and rape in this country going down. If violence was hard to simulate, and the only way to create images of violence was to hurt or possibly kill someone, I think we'd be much more likely to treat images of violence in the same way as we treat images of child abuse.
In the end, I think your argument may hold for fabricated or animated images of child abuse, but fails to do so for images of actual abuse. AFAIK, most images in circulation now are of actual children, and as such, we prosecute all images as if they were.
What about videos or images of gore where the authenticity may be hard to verify? Do these incidents of people or creatures being maimed or murdered cause people to be more likely to engage in the activities they see? Should they be illegal?
I think it depends on the prevalence of the activity. Right now, there are no recorded instances of someone engaging in violence or murder for the purpose of capturing it as an image or video for distribution. Most of the gore images on shock sites are coincidental video recordings of violent incidents/accidents or documentary images taken after the fact. These are not intentionally recorded "snuff" films, and to date, no true "snuff" film has ever been made, according to Snopes. In the absence of evidence of that sort of behavior, we should stick with the 1st amendment and not criminalize images of video of violence. In addition, it is possible for an adult to consent to being the subject of violence. That's not the case with children.
That's not the case for child abuse photos and videos. The articles linked in this post provide plenty of evidence of child abuse offenders producing images and video of their sexual abuse of children for the purpose of sharing it with other offenders.
In the future, if violence became more like child sexual abuse, I would probably support criminalizing possession of the images, initially narrowly, and then growing as the scale of the problem did.
Your statement here suggests that what is considered child porn always involves the abuse of a child. This is not the case. Many teens have been put on sex offender lists and had their lives trashed because it was found out that a girl/boy of similar age sent them a picture of themselves naked.
Also I wonder what the prevalence of fake/real violence in our society has on the demand for "snuff". You don't really need to seek out snuff films because you can easily see films that depict horrible things happening to people, completely legally.
I am not pro-child porn here, it just makes for an interesting philosophical/societal topic.
If you could make snuff films in a sustainable way (without disabling the actors and starting a murder investigation), they might well be made. Maybe even with willing victims.
There's a scifi/horror plot here somewhere...
On the other hand, violence is not illegal to depict, and there are many professionals who are experts in simulating violence without actually causing harm. This results in violence and rape in this country going down. If violence was hard to simulate, and the only way to create images of violence was to hurt or possibly kill someone, I think we'd be much more likely to treat images of violence in the same way as we treat images of child abuse.
In the end, I think your argument may hold for fabricated or animated images of child abuse, but fails to do so for images of actual abuse. AFAIK, most images in circulation now are of actual children, and as such, we prosecute all images as if they were.