Points of Discussion:
1) Popularity of Brokeback Mountain: Well-told story? Don't know, haven't watched. Controversial subject? Definitely. Controversy enough reason to justify popularity? Possibly.
2) Popularity of Male scenes vs. Female scenes: The "adorable" nature of male love is mostly a migration from the Orient. Then again, my bet is that the concept remains the same for men liking girl-on-girl scenes. If either of the subjects partaking was considered ugly, the scene wouldn't be as "adorable" or "sexy." I don't know the extremes of male love popularity, but when it comes to girl-on-girl, guys don't usually enjoy the scene unless they know they have a shot with at least one of the girls. The girl doesn't have to be straight, just willing. If not, it's no fun.
3) Shudo (Male) vs. Lesbian (Female): I don't believe there is a greater acceptance for either. Anyone vying for greater acceptance of either is usually vying for acceptance of homosexuality altogether.
Each is discriminated against in similar and separate ways. Violence can be a common thread.
Men who openly discriminate against gay men are more often than not a part of a subconscious social regime. Whether this regime is founded on principle, religion, or fear of personal security, it's numbers remain stable.
Men who openly discriminate against lesbians are usually one of two classes. Either they're a part of the ssr (as above), or they're just dogs who don't know how to stop acting like dumbass teenagers. In the case of the latter, discrimination is usually an attempt to idolize oneself among a greater number of peers who dislike homosexuals. It's social/interpersonal security.
Other reasons include a sense of alpha-male insecurity: an attempt to prove to others one's ability to dominate. If a man is rejected by a woman, he might call her a lesbian even if she's not. Then again, he may yet approach a woman he knows is a lesbian and suggest that he can turn her straight. If he's rejected by a lesbian, a man's reactions can be far more varying.
Men (mostly of the alpha-male subgroup) tend to need to experience multple women. Some might say that men and women have different reasons for slutting around. Although there might be different reasons for this behavior the difference isn't found between the sexes. Anyway, (that was a little off-topic).
The last possible reasoning for a man to dislike lesbian relationships is the fear that all women will pair off and leave the men behind. This is probably due in part to jokes about men being stupid and unnecessary.
I state the following merely as an observation as I'm not a woman and my views are not proven as far as I know. Women tend to discriminate for separate reasons than would a man.
If a woman discriminates openly, she's likely well-grounded in personal belief whether principle or religious. Women tend to be more accepting of change because it is in their nature to be nurturing mother-figures. A woman's discrimination is usually less severe and abrupt than a man's. They mostly imply a lack of understanding or age, but even this behavior doesn't supercede their desire to support.
Men and women who discriminate openly are rarely found to be of different orientation themselves.