I agree, hentai is fine if you're mature enough to realize it's a form of entertainment and nothing more, it's a way of exploring our own likes and dislikes, regardless of gender or sexual orientation. If a girl/lady/woman likes hentai, then good on them! I say do what you like, watch what you like and be tolerant of other people's likes and dislikes.
Plus, there is the added bonus of hentai often actually having a good story, unlike your standard live-action porn, which often has a shoddy plot, at best. Hentai very often has a story that is interesting, with or without the nudity and sex. Two examples are Mystery of Necronomicon and Kite, they both had good stories, with a little sex thrown in almost as what seemed like an afterthought. But anyway, I digress, like I said, I think hentai is a perfectly acceptable form of entertainment for a mature individual.