is that paying sex should be regulated. That is, instead of prosecuting it, make it legal because with that the state get's it's share and in return also provides security for people involved in the trade. Someone being exploited by employee is much more likely get a fair trial against said exploitation if he/she is involved in legal business than if it was illegal.
OK, lets look at different types of prostitution and likely effect of treating them like just another business
I'd say there are three major models:
1) Exploitation (drug addicts, illegal migrants, sex slaves and more) : Legalization will do very little, because this kind of model is based on exploitation of girls and low price category. They will stay in shadows because else pimps will have to pay fair salary, taxes, health check fees and more, more, more.
Society need to punish both organizers and clients, because it is nothing but a form of a rape. Even if client didn't know that the prostitute he used is forced to service him. He is a rapist and should be treated like one. Fining is simply not enough
2) Just another kind of work. We have an owner\organizer who gets money from clients and pays salary. Workers are free to leave. It may be a brothel, escort service, strip club with "private dances" or any other model
Only very left or very feminist will call this "exploitation" Legalization does make this scheme more comfortable for clients and owners and may take some clients from category 1 but you need a strict control to filter category 1 that disguises itself as category 2.
3) Self-employed prostitutes
They work for themselves, may pay some money for assistance with finding clients or getting protection.
Legalization (aka you need a license, you need pay taxes...) and so on is BAD for them. I imagine work interview. "Let me see your papers? Hmm... You were a part time prostitute during your college days. Interesting. We will call you later"