I looked up the word 'hentai', and the way you used it is incorrect. It's like using the word 'porn' to mean 'child pornography.'

There is also a problem with your argument itself. Child pornography is illegal because it involves harm to children, not to suppress people with certain preferences. If there are no victims and it’s just a fictional depiction, there’s no reason to ban it.

Personally I don’t really like people who are into that but that doesn’t give anyone the right to oppress them.