Bah, everyone knows my opinion on this but I believe that laws against all victimless crimes, including drug use of all kinds, are nothing more than Law Enforcement Employment Security Acts. Prohibition never works. History has taught us that. Education works. Tobacco use has gone from 60-70% of the population decades ago down to a small fraction of that. Legalize, regulate, educate.
Of course prostitution should be legal. As with drugs, legalizing prostitution assures cleaner, safer environment for both prostitutes and their clients. Prostitution-driven crime plummets... who needs a pimp when performing a perfectly legal service? Of course, vice officers will be twiddling their thumbs, so that isn't going to happen.
Adults have the absolutely right to decide what to do with their bodies, what to ingest in their bodies, whether it's healthy or not. Educate hell out of the population, use license fees and drug taxes to fund low-cost rehabilitation facilities, and help drug users in the same manner we now help alcoholics and those addicted to tobacco. Provide programs, support and assistance.