I don't, personally, think that prostitution is a good idea and would probably not recommend it as a professional choice to a friend. But, I don't see a valid argument for making it illegal.
Politically, I don't see any difference between recognizing a woman's right (woman of legal age) to have the freedom choice to do what she wishes with her own body when it comes to abortion, and the subject of prostitution. If you recognize a right of a woman to have an abortion and consider that decision none of your business, from where do you get the authority to determine that she should not be allowed to have sex for money?
edit: This post was not directed at anyone in particular -- only to those that are arguing against the legalization of prostitution, but are in favor of legalized abortion.