Off the top of my head:
Watching real child pornography should be illegal because watching it promotes it being made.
Watching real gory videos should be illegal if they promote the act being done to be done again. I'm unsure if it should be illegal if it doesn't promote more of the same kind.
How can you be so sure child pornography promotes more of it's kind but gore doesn't. Obviously, in either case, if you pay for it, it results in more being made, but if you don't?
It is so sick and horrible, but is it also their free choice to watch it? Then again the real death of another shouldn't be a source of excitement because humans have diginity. I want to say it should be illegal, but I don't know.
But you are so sure about child pornography. Why are you so sure about it but not gore? The only difference is that you will have more accidental gore than child pornography (as already pointed out by another), but besides for that I don't see much difference.
Videos which arn't real but are gory I guess should be legal. I assume this applies to some horror films (which I have never watched). I don't see why people would want to get a thrill from seeing another persons pain (even if it isn't real) but I guess it is their choice.
Fake child pornography should be legal if it doesn't lead to an increase of the real kind.
Supply and demand. A person can only consume so much porn, so the more of it that is fake, the less demand there will be for the real stuff. In general, studies have found decrease in sex crime correlate with the legalization of pornography in general, including one study that found a country which legalized child porn had a drop in child sexual abuse at the same time (they have recently made it illegal again so there is more study into if this will result in an increase in child sexual abuse or not). Of course, correlation is not causation, but good luck getting the IRB to approve an experimental study on this issue.
If it leads to a decrease then even more so. I would say people can't help their attraction and so giving them an outlet could be helpful.
How far can you dictate morality even when it is sick and horrible to the average person?
What is sick and horrible is so culturally dependent. I have arachnophobia, so when I saw a video of some other culture eating tarantulas, I got the strongest rush of both fear and disgust. I think I would be less traumatized by watching a video of a 'donkey show'. I've even seen a documentary on cannibal that included them eating a human, and that was less disturbing than the group eating a spider.
In some cultures (namely Western culture in the past), the average person would have found child nudity/erotica (which is labeled child porn these days) quite normal and artistic, but would have been horrified about porn containing adults engaging in homosexuality.