Prostitution was made illegal by the same source in which alcohol was prohibited in the early 90's.
Puritan ideology and bias.
The fact of the matter is that prostitution was legal in every Christian society to date until America happened. The Catholic Church even allowed brothels and such.
Defending dope
http://www.theologyonline.com/forums/showpost.php?p=4623004&postcount=105
and now prostitution: yep, a real conservative.
http://www.theologyonline.com/forums/showpost.php?p=4622948&postcount=101