When I was in Hong Kong, early 70s, prostitution was rife, it was also illegal, However, it was recognosed that the authorities couldn't stop it, so the girls were given a free health check, and if clean, were given a blue card and allowed to continue with their trade.
Any soldiers that wanted to go with one, to make sure the girl was clean, could ask to see this card, VD was classed as a self inflicted wound. The system worked.
Shame they don't use a similar system over here, legalise it, then the goverment could get tax off the earnings.