I can explain some of the double standard between the common mens attituides towards lesbians and gays.
Men don't like seeing men romantically involved with other men because they have grown up with it being referred to as the worst possible thing, absolutely unacceptable and repulsive and so they have internalised the general atmosphere of homophobia to the point that they have an unconcious physical reaction even when their concious mind is fine with gay people, can talk to and be friends with gay people it is witnessing the acts that revolt them.
Men like seeing very feminine lesbians. This comes from the same homophobic source. In porn they often have to "look round a guy to see" the things they want to see (quoted from a friend of mine). Seeing the same images of women without the men removes the confronting element. There is also a fantasy element (not actually believed by any guys I know but still a strong fantasy) that the women are lonely, giving each other pleasure for lack of a guy who can fulfil them and so the man can easilly fantasise about being that individual. Another strong turn-on for many men are women who are forward and open minded when it comes to sex and so lesbian acts are seen as a strong display of this from strong and powerful rather than dominant or submissive women.
Also men are taught to adore women and disrespect males, both other males and themselves. This makes it easy for a man to imagine that women would find other women attractive but harder for them to understand that anyone could find men attractive (it doesn't help that I have heard many women say that sort of thing either) and also why men find feminine lesbians acceptable but masculine ones very threatening.
I have seen some erosion of this phenomenon though as gay and bi men, effeminate men and strong masculine women are seen more in popular media more people become more acustomed to it and get over their hang-ups.. except for the more homophobic folk. I myself was a bit squemish about such things but, upon recognising my own hypocrasy was able to undo it pretty easilly.
Just look at other social double-standards.. men who sleep around are often lionised by their mates while many men and even more women rank the same behaviour amongst women as the lowest of the low.