More uninformed museings-
I remember a gay guy telling me that faithfulness was more of a concern to him than a hetero relationship, beacause guys like sex so much they are more likely to cheat. I also remember a bi guy telling me that same-sex attraction was of 2 types: kind of like looking in a mirror, seeing yourself- or what you'd like to be- in the other person; or, confirming your atractiveness by an admirer. To me, the hetero relationships seem different, like how can you aspire to physical characteristics of a different sex person? It seems like more of a challenge to understand and meld with a different sex person.
Ideas about the porn thing: 1) female-female stuff may be seen as generaly more acceptable/desirable/whatever because of historical norms about carnal desires and sin being intrinsic in the nature of women, right back to Eden-fruit-gate. Kind of like interracial taboos about sex. 2) Also, because men are generaly more overtly sexual, physical sex between women may be seen as less common therefore more desirable. 3) More astheticaly pleasing because its less 'messy'/dangerous (no ejaculate, etc. - I got this one from a bi woman). 4) Hetero guys are afraid that bi/gay guys are going to treat them like some hetero guys treat women (bad- I got that froma Kids in the Hall actor).