Much of illegal imagery involves teens who appear sexually mature, and those who enjoy viewing it are primarily attracted to adults. I dealt with that in <this post>https://celibatepedos.blogspot.com/2020/05/the-internet-watch-foundation-young.html. Here I focus on the illegal imagery of clearly prepubescent children.
To much of the public, the man who feels any degree of sexual attraction to children has forfeited his place in humanity and is nothing but a monster. Why? It is those who have such feelings who molest young children, and the attraction feels very unfamiliar. Yet scientists and clinicians who work with people attracted to children know it is a very different story (as do pedophiles themselves). It is typically in the early teen years that a boy becomes acutely aware of who he is sexually attracted to. For most it is adult women, and the world is well aware of the power of that desire. For a small minority it is adult men, and such boys typically feel great distress. They will try to convince themselves it isn't true and they really are attracted to women, but the coming-of-age stories of gay men make it clear that their attraction cannot be wished away.
Another small minority of young teen boys realize they are attracted to children. The feelings are just as powerful and just as inescapable, but the distress is far greater than what gay men feel (at least those in reasonably liberal communities today). Hearing of a teen attracted to children, most people react with horror and denial. There must be a mistake. There must be a cure. The boys must have done something bad to make that happen -- maybe they even chose it. But none of that is true. It just happens, in exactly the same way that homosexual attraction just happens. So let's be clear: the men who look at CSEM of prepubescents are not monsters, they are human beings, just like you.
What should such teens (and the men they grow into) do about their sexual attraction? To most people, the answer is that they must never entertain fantasies or masturbate with children in mind -- and nowhere does this look clearer than it does in the UK. In the UK, it is not just CSEM images that are illegal, but cartoon drawings of children in sexual situations and text-only fictional stories that describe children in sexual situations. IWF stresses that the images it removes are from a crime scene and involve a real child. But these other images/stories are not from a crime scene but are still illegal. Some rationalizations for those prohibitions have been offered -- maybe anyone who looks at such material is actually abusing a child and hasn't been caught. Maybe it will in their minds make adult-child sex seem OK and lead them to offend later. The evidence for both has always been weak, and within the last decade studies suggest that both are <just plainly false>https://www.researchgate.net/publication/325151499_Child_Sexual_Exploitation_Materials_Offenders_A_Review. But rarely do people find that out and say, "Oh, OK, I guess they should be legal then!" The gut-level reaction is still that it is wrong and it is good that it is illegal and men caught with such material (during the making of which no actual children were involved in any way) should suffer severe criminal penalties.
But even if you made your peace with pedophiles looking at erotic material made without any real children, of course many pedophiles look at images of real children -- at CSEM. What are they thinking? Men attracted to children cover the same range as the rest of humanity on just about any attribute you can think of -- except who they find sexually attractive. Some are mean, some are callous, some abuse children, and some post the material online. But a great many do not have those traits.
A true pedophile knows he must keep his attraction a secret -- if he reveals it he will be hated and ostracized, likely losing his housing, job, family and social networks. He quite likely hates himself almost as much as others hate him. He knows he will never marry or have children and will quite probably never have sex with another person, or his occasional experiments with adults will be frustrating and embarrassing. Yet he has a sex drive as strong as anyone else's. He would never abuse a child because he doesn't want to hurt anyone.
On the other end of the spectrum from those who film themselves sexually abusing children, a great many would never dream of accessing CSEM and are horrified at the idea that anyone else would. Others might dream of it but have good self-control and a fear of legal consequences. They will never seek out CSEM.
Then there are those in the middle. Imagine a man who is drunk and feeling lonely and horny on a Saturday night. If he's an ordinary guy, he brings up adult pornography to see the people and situations that turn him on. But suppose he's a pedophile. Let's call him Bill. Along with loneliness is a fair dose of desperation. He searches the web for images of what fills the same role for him -- CSEM. He finds them easily enough. He doesn't pay a penny. The videos show no evidence the children are being damaged physically, and they are smiling. He suspects they are not actually happy and are being exploited, but it's not apparent from the videos -- and easy to brush aside given his state of sexual arousal. He also knows that whatever the children suffered, it's in the past -- what's done is done. He knows that their suffering does not increase just because he looks at their sexual abuse on that particular Saturday night and masturbates to it. But after orgasm he typically feels deeply ashamed.
The attitude of the IWF (and much of society) is to be unmoved by this story. Looking at CSEM is wrong, there is absolutely no excuse for viewing, and it is right if Bill goes to prison.
Let's consider a couple other of our fellow humans. Joe is a smoker, he has heart disease and also has two young children. The doctors tell him his smoking is threatening his life. He tries to stop but doesn't succeed. Mary is overweight, with diabetes, and her life is in danger if she doesn't lose weight, and she also has two young children. She tries to lose weight but she doesn't. So what the fuck is wrong with Joe and Mary? Aren't they selfish assholes? Perhaps we should put them in prison! Various ones of us may condemn them to varying degrees, but most of us retain a considerable measure of sympathy. We don't consider prison because we know why Joe and Mary are failing. They are imperfect humans under the sway of powerful psychological forces.
Now let's compare them to Bill. He has no prospect of love or satisfying sex in his life but has a strong sex drive. Sometimes he looks for erotic pictures of children on the web and masturbates to them but afterwards feels terribly guilty. Why does he do it? Because he is an imperfect human under the sway of a powerful psychological force.
Let's also examine the harm caused by Joe, Mary, and Bill. Joe and Mary's failure to change may kill them, leaving orphaned children who will bear psychological pain for the rest of their lives. As for Bill, no child is going to know he had sexual thoughts about them. Some children in CSEM videos feel upset to know that a record of their sexual abuse is available online and men look at it and think sexual thoughts. But Bill is just one of a group of thousands who collectively contribute to this distress. The "marginal harm" of his viewing is very close to zero. Joe and Mary have done far more harm, but we sympathize with them. Bill has done very little but faces prison.
Let's also remember what Bill did NOT do while under the sway of a very powerful psychological force. He did not molest a child. We know that ordinary men under the sway of that same force will sometimes make unwanted jokes, leer, whistle, harass, or grope women, things much of society strongly disapproves of but that rarely lead to prison terms. Bill did not do any of those things.
Child sex abuse is a terrible crime. Recording it and posting the recording for the world to see is also a terrible crime. There is no excuse for looking at CSEM -- it is wrong. But most of the time, it is not the act of a monster but of a weak and imperfect person who did not intend any harm or cause any direct harm. We as a society should choose the appropriate penalty with that in mind.