The fact that male homosexuality is still extremely taboo, but cannot really be accounted for in terms of evolutionary psychology, means there must be other factors at work.
I think another reason for the fear surrounding sexuality in general (rather than only female sexuality) is the fact that sexuality is the greatest expression of our animal nature. Civilization can be understood as the 'taming and control of nature', both in terms of our environment, and in terms of our own behavior. Our sexual nature is a part of us that is vital to our existence, and yet totally beyond our control. It is 'the beast within', and the fear is that this beast could take over and destroy our neatly constructed 'civilized' lives.
From another perspective, most of the sexual rules that dominate western civilization have their origins in the Bible. Leviticus 18 contains most of the codes by which the majority of people in the west live, and it is also here that we can find many of the taboos. They include incest, homosexuality, and bestiality.
Leviticus 18 - PassageLookup - New International Version - BibleGateway.com
Interestingly, the passage ends, 'Everyone who does any of these detestable things—such persons must be cut off from their people." The intent, therefore, is to control people through fear of social ostracization. This seems to me to be the root of sexual fear, the fear of 'what will other people think?'.
The passage from Leviticus begins by saying, "You must not do as they do in Egypt, where you used to live..." This implies that many of the things currently considered taboo where actually once freely practiced in Egypt - i.e. bestiality, incest, and homosexuality. There would be no need to lay down laws against these things unless people were actually doing them, so this tells us that, of course, they were!
The sexual laws in leviticus were created so as to prevent the early jews from engaging in some of the sacred sexual rituals of other civilizations they came into contact with - such as the followers of the god Molech, who later became synonymous with the devil. They were intended to stop people from defecting to these other (perhaps more fun) religions. In other words, they were an attempt to control a large group of people by controlling their sexual behaviour - claiming it was god that was forbidding them.
I think a large part of our cultural fear of sexual expressiveness, and the fact that today we still consider sex 'naughty' 'nasty' and dirty' - even if these words are often meant in an enjoyable way - is a result of the sexual repression handed down to us from these early examples of social control.