I'm not sure we can 'blame' society for this. All of my friends know I'm married but none of my friends (swingers excluded) know that our marriage is anything but normal. Society tells me swinging is somehow wrong, if I were trying to run for office and this sort of thing got out I would never get elected in most parts of the country (regardless of party) yet we do it anyways because we think 'society' can cram it :p . If I had the SLIGHTEST desire for a homosexual experience I would most likely try it, but to me its about as appealing as fucking my dog (and lets not see THAT thread again ).
At any rate I don't see it as a double standard. Most swing clubs (and swingers if you look at adds) have no problem with girl-girl but big problems with guy-guy. This isn't a sexual liberation issue, but a 'what do the people want to see/be part of' issue. I want to be 'turned on' and seeing to guys having sex has just the opposite reaction to me. If I wasn't in the majority on this one clubs wouldn't have such rules in the first place.
I would refer to my wife as 'barely-bi' and would rather leave it then take it, but she has never been turned off by seeing two women together. Society didn't prepare her for this, there wasn't any female kissing on tv when she grew up, and lesbians were thought of as only gym-teachers, unattractive women, and athletes. At the same time, she is turned off by seeing two guys together.