From under my Sigmund Freud hat: we make it taboo in order to repress it. Left hand vs right: that's in "Lawrence of Arabia," too! I remember my parents laughing about it before I "got" it. Sex in front of the kids: see "playing refugees" under the blankets in Amy Tan's? Joy Luck Club? Woman Warrior? as her parents called it. Biological assymetry: as one who believes "we actually are all One" I run into the whole Gnostic issue of male/female and which comes first or if that's a chicken and egg quiche. 😉