Others have already waved the wikipedia card, but I feel that there is one aspect which deserves clarification.
Above all, we should divide prostitutes into two groups: sex workers (who have, for whatever reason, chosen the profession); and the victims of human trafficking. In my mind, trafficking is no different from slavery. It's a vile thing. A sex worker, on the other hand, can choose to have a pimp -- but one is not required.
I have absolutely no problem with law enforcement cracking down on trafficking. Those people are not selling their services out of their own will. But trying to mandate morality by law makes my hair stand out.
I happen to believe that indiscriminately cracking down on all forms of prostitution is simply a waste of resources. The similarity between aggressive pro-lifers (who want to impose their own views on how women can use their bodies) and anti-prostitution zealots is not that big. Control in the name of morality ... or just in the name of their personal delusion.
Makes little practical difference.
That said -- and it's amazing how many people are so stupid -- it's very difficult to successfully ban transactions that are, if not morally voluntary (ie the whore could be trafficked), at least voluntary in the moment. The same applies to drugs, prostitution, and sex. As Bill Hicks said: We had a war on drugs, and drugs won. (Though most republicans don't even believe their own bullshit; the number that have smoked a joint or who look the other way when it's their daughter knocked up at 17 or their mistress or their wife is pretty astounding).
That phrasing usually refers to trafficking. Let's do some numbers.
In 2000-07, there were 1,500 identified victims of trafficking in the USA - total, not a year, and including both sex and labor trafficking.
http://www.washingtonpost.com/wp-dyn/content/article/2007/09...
Arrests alone for sex work is on the order of 100,000 a year (confirmed). An estimate puts the number of prostitutes at 1-2 million.
http://prostitution.procon.org/view.answers.php?questionID=0...
No doubt trafficking is a big problem in many places - there just isn't any evidence that the US is one of them.
If there mere fact that there exists sex workers who are in the trade not out of their own free will is sufficient to outlaw the trade entirely, there are quite a few trades that would need to be outlawed.
How many? What percentage? Citation needed.
Weasel words will get you nowhere.
What puzzles me immensely is that in progressive countries like Sweden the push against prostitution is almost worse (although with the angle that the buyers are criminalized), and that feminist women don't see that decriminalization would have a mostly empowering fact for the prostitutes (who are mostly female).
I can see that it is an icky subject for many and how people who fight against the objectification of women might fall in the trap of thinking that selling your time for a fee might contribute to that.
However pimping out my brain for trying to make people spend their money on ingame purchases is way ickier to me.