What are some arguments for decriminalizing people selling sex while criminalizing the purchasing of sex?

Sometimes minors are forced into prostitution, and should not be held criminally liable 
Many people in the sex trade want to leave that life and a criminal record impedes their progress
Turning to prostitution is often the last resort of a person who is impoverished, and poverty should not be against the law
If law enforcement depresses the demand for the sale of sex (by going after those who would buy sex), then prostitution rates may drop