That makes sense. I suppose I'd need to know more statistics before arguing further, but I still say that even though I am an opponent of that kind of material, I am a proponent of allowing people to decide for themselves what is and is not appropriate material. Further, I think that governmental bans on anything do two negative things: firstly, it encourages the banned object/substance/material to become that much more appealing to a wide enough section of the population to INCREASE it's demand, thereby secondly increasing the rate of crime. Look at prohibition, for example, or the US's current criminalization on marijuana- otherwise law abiding, non-violent people are being thrown into the criminal punishment system for things that are largely harmless which taxes the system's resources. And for what? A little pot? Or in this case, a drawing of sex acts? It seems silly to me.
On the other hand, if it is true that sex crimes are under-reported in Japan, and if this material has something to do with that, I would reverse my position in no time because it would have shown itself to be harmful enough to warrant its ban. I'll need more information before that happens, though.
EDIT: Just read your last edit, and I have to say that it is convincing. If we are to look at it as hate speech, though, how then do we stand on film pornography which depicts the same? Since porno is SUPPOSED to be fantasy anyway, and is allowed in the US that I know of to show that kind of violent material- which I maintain, I personally detest- then should we start drawing lines there, too?