Just about every straight person I have talked to about art has professed that the female form has more artistic merit than the male one. They gleefully describe how a female’s shape is more interesting to paint/sculpt/view. In my early days of coming out I accepted this along with many other declarations along those lines. At the time this bothered me but I didn’t have the words to counter it. But there was one other aspect to this that made it difficult for me to argue: you see I personally don’t have a problem with the female form. I am definitely gay, but I still see beauty in the feminine physique and I don’t see the need to find fault in women just because I’m a gay male. The fact that the heterosexual world seems to be caught up with this silliness is their problem, not mine.
Well, in some ancient cultures it was acceptable for married women to have affairs with other women but not with men, because then their childrens' paternity wouldn't be in doubt. Today, in most cultures, it has to do with power.
Plenty of people have expressed better than me why so many heterosexual men feel threatened by the idea of men having sexual attachments to other men. However, in the case of women the dominant group finds lesbian action a turn-on so it goes without saying that too much negativity about it would put members of that group in a bit of a bind. Or as the loser-protagonist in "Married With Children" put it: "There's nothing wrong with a woman having sex with another woman - as long as there's a man watching."
That's not to imply actual tolerance for lesbianism among homophobes. Two women here in Missouri were denied an application to be foster parents last year, and took it to court. The court ruled that the reasons for their being denied - their sexual orientation - were irrelevant to the welfare of the children and our homophobic State district attorney is still in a snit about that. The prejudice against lesbians is more subtle.