My Googling suggests that in Vienna where prostiutes have to be registered around half of the registered prostiutes are victims of human trafficing.

The policy of registration which as of the beginning of this months also entered German law, doesn't seem to result in an elimination of prostitution that shouldn't be there.

I think your arguments also rests on the fact that there are programmers who actually want by their own volition to do the programming jobs that customers demand. On the other hand there are prostitution services that are demanded by customers that very few woman actually want to do.