“Discuss, based on your own and other’s experiences, how kids learn about sex.”

This question was posted as part of the assignment for my Theories of Personality course for this week. I found myself wondering about  why sex is such a forbidden thing in society and why sexuality is often obscured and euphemized. Sex is often grouped with drugs, why is that? What is so absolutely horrible about sex that children are protected from it for so long that they feel they must experiment to find out about it?