Rather than accepted, female bisexuality is “encouraged” on the sole grounds that it be palatable to straight men. Bisexual women are presented in hypersexualized contexts, as sexual objects for the hegemonic straight male gaze, while directly or covertly appealing to a quasi-pornographic fantasy of a (two females and one male) threesome, and while also reassuring us that these women are not really bisexual, but are simply behaving so for the satisfaction of the presumed male spectator.

Shiri Eisner, Bi: Notes for a Bisexual Revolution, p.159 (via bisexual-books)

ditto for lesbianism tbh (see the entire genre called lesbian porn)