When, a few years ago, I was invited to re-edit the 1972 manual, The Joy of Sex, I expected to be reporting good news. Given increased societal tolerance, more effective contraception, better health care and more stringent definitions of abuse, I hoped to announce that the world was a far more positive place to be sexual than when Joy was first published.

Not so. On the contrary, particularly for women and particularly in developing countries, sexuality now seems endlessly problematic. On one …