Don’t the Occam’s Razor’ish explanations suffice for explaining the fear of female sexuality: we see time and again that males of species attempt to control the reproductive activity and choices of females. There are species of birds in which the male, after mating, secretes a substances that plugs the female’s entrance for a period of time, giving his sperm a headstart over any immediately following competitors. The human male, without the tremendous physical power advantage of the silverback and hobbled by the cunning of human thought, no doubt lives in a perpetual state of anxiety about reproductive success and “worse”, “wasted" parenting effort. The more the female takes pleasure in sex, the more threatening it is!
Of course human cultural/mental evolution has reached the point where men are terrified of having children while still wanting to control the reproductive activities of women :-).
—ravi