You still can't force somebody to prostitute:
http://dejure.org/gesetze/StGB/180a.html"Ebenso wird bestraft,wer...eine andere Person..., zur Prostitution anhält oder im Hinblick auf sie ausbeutet..."
I think any auto translation will get it wrong because of some legal terms. So that is my approach:
"Also is to punish,... someone who ... encourages another person to prostitution..."
So cutting down someones welfare for not working as a prostitute is therefore illegal.
By the way, the whores had to pay taxes even though their work was marked in legal terms as immoral. It was just assumed how much they get for their job and then taxed.
In a free community everything that is not illegal by law is legal. No matter some people have different moral views on something. Prostitution is not prohibited in Germany.