<< Prostitution brings Drugs brings Crime. >>
...they bring crime because they are illegal, hence crimes on their own merits. Legalizing both would remove the "bringing crime" factor.
"Fvck!ing is legal, selling is legal. Why isn't selling fvck!ng legal? Why is it illegal to sell something that you can give away for free?" - George Carlin
EDIT: Damn, my whole post made pointless by other posts. Should have just RTFT