With prohibition come black market crime and exploitation, while legalization would bring regulation and unionization.
Please don't bring prohibition into this. They suddenly made a substance people had been drinking for centuries illegal (which people were easily addicted to). Not only this, but it is easy to make alcohol, as a matter of fact one extremely potent alcohol type. Now they tax the **** out of it (and tobacco) which lowers the cost. Also prohibition is another example of our human nature and body working against logic and reasoning (proving my point).
It isn't federally legal in Nevada (like pot in Washington/Colorado) meaning the FBI can sill come in a hammer down on the prostitutes if a problem arises (such as the leader of a gang who runs a brothel but they can't get anything on him but that).
Regarding HIV rates in Nevada please read this link http://resources.lawinfo.com/en/legal-faqs/criminal-law/nevada/index.html
It explicitly details that you will be charged with a Felony if you engage in intercourse with an STD, which means they are still controlling our bodies for or safety. (Much in the same way a vaccine is required)