The vast majority of what may be considered CP is a record of the live abuse of a child. Understandably it would be distressing for survivors to learn, years later, that not only does such a record exist but the public is gleefully reliving their trauma and spanking off to it. Consider that distributing so-called revenge porn is illegal, and that this is far worse than that.
People are upset by many things. It doesnt really follow that whatever upsets people should be illegal simply because it upsets people.
But what about simulated CP? The principle objection here is that viewing CP whets the appetite of pedophiles, making it more likely that they'll go after real children even if it serves as an outlet in the short term.
Whats the proof for that?
In the aggregate this may or may not be true, so I would add something else to this: that porn has the capacity to "confuse" some viewers.
I once came across an anecdote on the internet from a mother who invited people over to her house. Her roughly 2 year old daughter, who hadn't been potty trained, walked around shirtless in a diaper. One of the male guests, dead serious, asked her if said 2 year old daughter was coming on to him sexually, which was the impression she gave him just from existing in a shirtless state. The mother was understandably freaked out by this guest and never invited him over again.
By this logic, you should ban children from going to the beach.
But again, if your argument is that child porn turns people into pedophiles, thats obviously false, as much as gay porn doesnt turn people gay.
But if your argument is that pedophiles are more likely to offend if they watch child porn, what possible statistic do you have to support that?
This guest would've been open to the prospect of molesting a 2 year old, because he was willing to believe that a 2 year old "wanted it" or even had the capacity to "ask for it". He was different from the kind of sexual predator who was perfectly aware of the morality of his actions and just didn't care, which begs the question: how could a grown man of reasonable intelligence come to believe what this man did? The answer that makes the most sense is: he watched CP where the child appeared to enjoy it, and applied this supposed insight to his dealings with children and babies around him.
Thats a story, not any kind of valid statistic. Its quite possible that even if person didnt watch child porn, that he would get same idea due to sexual attraction he has. In fact, some countries which banned all porn and dont even have internet to watch cp still have lots of child marriages. Afghanistan, for example.