I think that, from a purely moral stance, hentai is more acceptable. It does not involve actual individuals engaging in sex in exchange for money, it does not foster a business based on people having sex so that a third party can watch them for their own amusement, there is no risk of STDs being passed between the "actors", and no poor wife or mother has to go to work, get gangbanged by twenty guys for practically chickenfeed, and all the while be thinking "I'm cheating on my husband" or "What if my kids saw me like this? How can I tell them that something is right or wrong when I do this for a living?" And for couples who watch porn, or individuals concerned about their partner's porn watching, its not like they're "cheating" on their partner with the woman/man in the video. Its a 2D drawing designed by one person, animated by several others, and voiced by another as well, not an actual person, so there's no abuse, coercion, infidelity, or danger at all. Now, if you're of the belief that any pornography is immoral, and that masturbation is as well, then that's another matter.