All normal men desire -- quite apart from a stable, loving relationship -- an endless string of novel sexual partners. Most men don't interest women in this activity, because they aren't high enough in status for women to be sufficiently attracted to them. Even for those men who do interest women, extra-pair sex is fraught with danger (not least women wanting to steal them from their partners). The most straightforward and honest way to satiate the desire for extra-pair sex is to pay for it. But if men pay for extra-pair sex, then we intuitively see them as having 'broken the rules', in how we naturally 'police' the male hierarchy. This is why there is such a general downer on prostitution. Yet the exploitation here clearly is not of the women, but of the normal desires of men: men are exploited by women for money."