If that were the case, you would expect to find that legalization causes harm reduction. Evidence has already been presented in this thread that this expected improvement has not occured wherever prostitution has been legalized, so I expect you might need to rethink your conclusions.
I think another thing none of us really addressed is the fact that the illicit, daring, forbidden, risqué, and/or criminal is exciting and enticing for many. Even where prostitution is legal, there are those who are used for prostitution who work as illegal prostitutes, or as occasional prostitutes. There are those who are straightforward sex slaves, especially young children, and then there are those reports of children who are sexually abused in chat rooms and via video cams for the gratification of people continents removed who pay via credit cards. These children a prostituted by their families and can be assumed to be victims of prostitution too.
The billions of dollars that the illegal sex trade generates a year prove that those who can afford to pay for the brutalization and victimization of children and adults coerced, forced and threatened into prostitution/ porn care little about the objects of their sexual urges. (And yes, I am aware of the fact that not all prostitutes are female and not all users are male, so there is no need to belabor that fact.)
Still, if prostitution is decriminalized for adults and regulated like it is in various countries, then there will be at least some prostitutes who can benefit from working in a regulated industry. I go with the idea that even if it benefits only a minority, it still benefits someone. It certainly will not lead to a notable increase in the number of prostitutes available. I have yet to meet a 12 year old who happily embraces a future as a sex worker. And yes, I have met a few, the youngest being 10 when her father started to rent her out to his friends for some drugs, which brought her to a correctional facilitya place she rather enjoyed staying at
.then there was the 16 year old who was so happy to be released from the same facility because her boyfriend/pimp was going to wait for her at her mothers house. She was found dead in a dumpster 4 days after her release
or the girl who worked so hard to get a high school diploma while in secure care and was shot dead a week later by her pimp who had sold her to another pimp in another state while she was locked up. He shot her because she refused to get in the other mans car.
What we need to vigorously prosecute and severely punish is the pimp, the panderer, the madam, the filth who profits from selling the bodies of those they control. And locking up the users wouldnt hurt either; after all, we do it to the prostitutes as if they were the only ones taking part in the crime.