Not that I have a problem with people reading yaoi, but here's my two cents.
According to who? I work at a sexual education centre and in fact I just met a female porn director this weekend. You say that there are depictions of women being raped in porn. Well, guess what? There are depictions of men being raped/abused/humiliated in porn too. They're not very hard to find.
Yes, I agree that the majority of porn is marketed towards men, but saying that porn is "for men by men" and then using this to DEFINE porn is a gross generalization. Saying that porn is for men by men is like someone saying "romance novels are for women by women because women enjoy reading about relationships" -- a blanket statement that does not define what the term really means. Romance novels are marketed towards women, but that does not mean a romance novel written by a man and marketed towards men is not a romance novel.
Moreover, you seem to have a problem with pornography and "whores". Females and males who work in the porn industry are, in fact, real females and males. Some of them may have chosen to work in the porn industry; some may enjoy their careers. But consistently maintaining that pornography depicts "whores" (an extremely charged word, by the way), are you not perpetuating the belief that people work in porn should be dehumanized?
In 2003, Playgirl's gay readership was around 30%, according to Wikipedia. Women are still the main audience of consideration of Playgirl. In addition, by citing Playgirl's more recent trends, you are ignoring the fact that in the past, before Playgirl's gay audience grew, Playgirl WAS marketed exclusively to women.
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Moreover, you claim that yaoi does not represent gay men because the characters do not identify as gay. I would argue that yes, they do not necessarily represent men who actively identify as gay, but on the other hand, they do depict same-sex male relationships. In our culture today, you do not have to identify as gay to experience marginalization. We live in a heterosexist society - a society in which heterosexuality is generally taken to be the natural, the norm, and the superior - and men who have sex with men (MSM) are a historically marginalized group, regardless of whether they identify as gay, bi, or otherwise. Depicting MSM in yaoi IS misrepresenting MSM - characters in yaoi don't have to deal with feelings of being oppressed, marginalized, or silenced; they do not have to fear being discovered; and in real life MSM relationships there may not be a "seme and uke". Since you are so contemptuous of women being misrepresented in porn for the purpose of men in a patriarchal society, I wonder why you do not feel the same way when another type of people, MSM, is misrepresented for the purpose of women in a heterosexist society.
In the same vein, women who have sex with women are a marginalized group, and depicting girls having sex with girls in porn - whether they identify as lesbian/bisexual or not - do not change the fact that same-sex female relationships are being misrepresented.
Finally, if the only purpose of depicting men in yaoi was because they are "blank slates" and "cannot be whores", why are genderless beings not used? Or a third gender?