It will be the legalization part, due to fact that the government will always want to keep their hands on the money.....
The current legislation is faulty on that it makes the sex worker legal, while saying the client is illegal. There could be a arguement that if something is illegal, then all parts of it are illegal. So make both legal.
The thing is that there is a drive to get rid of underage prostitution, and trafficking people (indentured slavery). Which is people taking advantage of people and making a living off of them. The problem is no one is really going to talk because the victims are scared to talk.
Look at an escort agency, how does anyone know that they are not part owned by organized crime. Its hard to believe in this day and age they are not, when historically they were. What was the transition from organized crime to independant brokers (who owned escort agencies)?
The thing is sex sales. There is lots of money involved with it.