This sounds like a job for Ten Foot Pole Man!
But I don't think the world is ready for that hentai.
I've thought about it like this:
You have a depiction of gory violence in a comic. It's obviously meant to entertain your audience in some way. In more twisted pieces of entertainment (such as "Postal" or more recently "Hatred,") you have games where the ultimate goal is to kill as many relatively innocent people as possible in worlds more or less similar to reality.
These depictions even go so far as to allow you to do such things yourself. So it's not something where the protagonist of a book is going off to massacre a town while you read it: you, the player are given the option to do so (i.e., in playing the game at all) and then the player actually does these in a form of simulation. Men, women, children…all slaughtered in these sorts of games…by you.
Of course, if you know more deviant forms of pornography, you know there's a lot out there on violent forms of forced sex including unrealistic tags like "All the way through." But there's also tags that are quite realistic and explicitly state that the scene is that of a rape.
So if violence is allowed against weaker, innocent humans (after some controversy) where you actively instigate such behavior in realistic video games with voice acting, then why would that make less realistic depictions of minors illegal?
The simple answer is due to morals that change or don't. Most people in the US see sex in a different light than violence. Gender, sex, and identity is attached to a lot more than simply physical well-being. People kill themselves due to the frustrations of not being straight and/or cisgender, and this isn't even considering any discrimination or bullying. Sex is touchy, so to speak.
So as long as legislators and their constituencies (and their fundraising entities) feel a certain way, then laws will likely stay as they are in the US at least. Other countries like Australia may be on a different track. It's hard to say what the impetus would be for legislators to say "We should allow that Japanese loli porn over there back here in the US." I think you'd have to find a consistent stream of studies that show that pedophiles are much, much less likely to commit sexual crimes when viewing lolicon or shotacon at their leisure than if they aren't.
With actual CP, however, you're exposing minors to the direct gazes of others for sexual pleasure. If those children knew what people were doing to pictures or videos of them, they'd eventually begin to have a very different (at best) view of sex, one which may not be very safe when they begin to learn about their own sexuality and realize they're very attractive to a lot of people much older than them and their age as well. Teasing a man by showing off cleavage is entirely different from doing so when you're not developed enough to have cleavage yet.
Children shouldn't be shielded from sex altogether, but sex is something that needs to be exposed to children at a reasonable rate based on their maturity. And being a porn star (willingly and especially unwillingly) before you're ready doesn't seem ethical with that in mind. That's why I don't think you'll ever see even indirect CP be allowed in the Western world as we know it, and why I don't think you'll get a whole lot of clarity legally regarding depictions of it.