(in response to the linked article)
Another thing I would add is that while prostitution itself is a misdemeanor, efforts made by prostitutes to protect each other for safety falls within the scope of pimping, a felony. Lower personal risk means higher legal risk.
Not as a reason not to legalize, but a challenge in legalization that I see is in the area of contrast and parental rights / obligations. To my understanding only in recent years at the Bunny Ranch in Nevada girls may turn down offers by clients without penalty. Previously if a girl did not want to serve a client she would be held liable to the house for their share of lost profit. Not wanting to put girls into uncomfortable situations, girls are free to accept or decline offers as they please.
But what if this came down to a legal battle? In the exchange of most goods contract law can provide equitable relief on unique goods and services. How would the law remedy such a situation as in my experience every woman is unique in both beauty and talents.
Also, the US has unique anti-discrimination laws from other countries. If a girl does not want to be with men but only women, has issues with people of certain cultures, only want to be with older or younger clients, married or single clients? How do we address and remedy these civil rights issues when the law needs to be blind? Should sex workers get a special pass?
Also, would a sex worker that gets pregnant, despite all precautions, be entitled to the same child support as in other circumstances? Is it an assumption of the risk? Could abortion as an individual policy of a sex worker be advertised? Could it be legally enforceable? I would think that if it wasn't a legally enforceable provision of a contract (with advertisements being 'offers') then it could not legally be advertised, but it still makes the matter complicated. What risks would be assumed by the client and by employees?
I am not a fan of anti-bigamy laws for many of the same reasons listed above, and while I reject the common "ethical reasons" for a ban on bigamy, I see the greatest challenge being a legal one. As if family law is not complicated enough.
Finally, a major challenge I see is from liberal progressives that still hold egalitarianism as a social ideology and goal. I agree that many people get into prostitution because there are low financial and educational barriers to market. The most well educated and subsequently skilled sex works are always going to make the most money as in any business, but I am certain on the job training is always allowed. Not to mention that since sex work is typically commission based, brothels would need to be having exceptional difficulty with someone to turn them away. Most sex workers not bringing in good money get out of the business first. I believe all people pick goals based on their circumstances, but to an egalitarian opportunities that exist in nature for poor people are immoral and "unlovely". Thus, while people have sex for free, this punishment where appropriate to apply is seen as morally equitable.
Defeating socially conservative opposition to prostitution might very well be easier.
Recognizing that, sex workers rights is an issue that is exclusive to libertarians. "centrists" will go along with anything, but the further you get from the center either left or right I expect one to find a more difficult time getting actual support for any real reform. Even in this age of budget crisis, solutions, imo, have become even more aggressively partisan. This leads me to believe that an issue such as sex works rights that do not split on the political line, despite having very different reasons for supporting their position, I see it even less likely in this current environment that anything will change in the near future.