As said, whatever the moral arguments on this activity, it must be said that prostitutes do provide a service, be it so sad, kerb crawling characters, but more importantly to those who if not having this safety valve available, might well become a danger to women, young girls, and even children, if denied this outlet. The problem (as seemingly the law's hands are tied) is where these activities could take place and give least offence/annoyance to city residents.
One possibility could be to direct them to the poligono. The place is deserted at night, no residential homes to find reason to complain a nice, dark, deserted area where these nocturnal meetings could best be made.
Yours sincerely, Graham Phillips