“When it comes to wine, women and song, wizards are allowed to get down and croon as much as they like.” (Sourcery)
Wizards don’t have sex. Except of course where sex = biological gender because wizards are male in almost all instances and will argue any exceptions out of existence.
The celibacy of wizards is an odd quirk of Discworld magic which regularly returns as a running joke. However, most people (including the wizards themselves) are hazy on the ‘why’ behind the sex ban. Is ‘No Sex Please, We’re Wizards’ a rule of the universe, a rule of Unseen University, or more of a guideline?
We’re offered several answers over the course of the series, contradicting one another, and awash with flagrant heteronormativity. Marriage, sex and procreation in the Discworld are inevitable and interchangeable consequences, it seems, of men and women being allowed to come into contact with each other.