Asimov said:
Well, I think that the only reason prostitution shouldn't be legal is STD's, but that can be dealt with because if brothels became legal they would have rules, like maybe the mandatory use of condoms or something.
I don't live in the part of the Netherlands that has legalized and regulated prostitution, but it's my understanding that the girls that choose to work in that industry have to comply to certain standards, concerning regular health check-ups and prophylactic use. I'd also assume that those countries, having a different tack on drug-use makes it more difficult for many people that work in the sex industries to be manipulated into truly horrific situations by fucking with their drugs. Considering how common those stories are in North America, and how closely those stories tie into organized crime and gang activity here, I'd say that maybe considering the model applied throughout Northern Europe might be something to look into.
And no, for the highly politically incorrect point:
Marriage, or at least the more-archaic, curently-less-common, highly patriarchal, 'stay-at-home/home-maker' variety has more than a few similarities to codified and acceptable prostitution; a girl got married, started putting out, and in return, had her room and board paid for, and didn't ever have to work again. That's besides the fact that mistresses are generally an accepted facet of many societies, barring the countries that are heavily affected by the Judeo-Christian and Muslim religious models, although that's hardly a clean pass, either. Most of European society has more liberal and sane views concerning mistresses, and even some Muslim societies will turn a blind eye, provided that the mistress does not indicate any weakness in a given male. The simple fact is that a mistress is only a bare step away from being prostitution, but it's safe because so few involved would admit there was any negotiation prior to the beginning of 'business'.
Hell, Japan has had a codified and highly respected system for a long time, in geishas, although the sex is/was more typically a very background concern with that system, as geishas were primarily sought after as highly-sophisticated and intellectual gentlemens' escorts first, and highly talented sexual partners as a very distant tertiary concern.
Also, just a legal note that came to mind, while writing this: in Canada, the sale of sex is not actually illegal. The solicitation of sexual acts for money is, however, which creates a catch-all sort of arrangement, where filming porn can be a risky proposition, too. I've seen at least one just-barely-better-than-handicam movie in which there's obvious Canadian money being offered to 2 girls, in exchange for taping them being sexually explicit. I'm not positive, but I think if the girls had visibly accepted the money after the (clearly) audible conversation concerning the transaction, it would have (technically) been prostitution.