Flyhelico,
Whilst you logic seems to fit the title it is not that simple.
As a Private Pilot you are not, legally, allowed to profit from the action of excercising your priviliges of licence.
As a commercial pilot you are. Whether or not you wish to 'prostitute' yourself in the vague hope of putting yourself ahead of your peers with respect to the all elusive first job is entirely a personal choice.
The Captain is responsible for the safe conduct of the flight. End.
The Co-Pilot, if he has passed base training, line training and an OPC/LPC has the same responsibilities as any other co-pilot anywhere in the world. The fact that he is 'paying' to be there doesn't make him a 'student' or any less responsible for the lives of the passengers.
As I have said before I disagree strongly with P2F. I feel that we are gaining an era of pilots who don't necessarily have the best skills or temperament for the job but have the deepest pockets.
There is, sadly, nothing illegal about the practice.