The main character is a lesbian, yes, and also is rather perverted, but I don't think the author is trying to make that connection between homosexuals and perversion at all. After all, she has that priest who is just as perverted as the main character, but still isn't really a bad guy (the perversion is more or less mild). I think it's just that she likes to give her characters very strong personalities (Mariya, for example, is a straight guy, but he's a lot worse than she is, so . . .).
And just for the record, I think your sympathies are supposed to be with the main character, not the evil cross-dressing guy who tries to rape her. He's supposed to be portrayed as sadistic, and you are supposed to feel sorry for her. Just because she's a lesbian, and he's really mean to her, doesn't mean that the mangaka is trying to say that it's okay to be mean to lesbians, or anyone for that matter. Mariya is supposed to be the villain.
I for one, really enjoyed the humor of it and the relationship between the two main characters. It's refreshing for the main character of a shoujo-esq manga (I know it says seinen) not to fall for the guy (at least, not yet) who abuses her. So often in these mangas, girls let guys get away with crap and they still love them anyway, but not this one.
I gave it an 8 because it could be deeper, but for a light laugh, it's a good read.