In places where drug use or prostitution are illegal there are usually interest groups earning quite bit via the penal system or just plain stealing people's stuff because they were involved in drugs or prostitution.
So logically speaking it should be officially accepted as a profession and managed by the health department in order for the sex workers to not suffer as much. Then you can also apply the same controls to sex trafficking as you do to the non-sex shadow work force.
Portugal's health system allowed them to legalize drug use and create a healthier society and decrease related crime. Let's face it, if someone wants to smoke crack or pay a sex worker, they will do it regardless. Might as well control and earn money the usual way like liquor taxes.