Although I appreciate the comment STP, consider what happens in an operating theatre.
If a medical procedure goes wrong, all the apprentices get out of the way and the experienced professionals do the job. Someone's life is at stake after all and they deserve the best care. We don't have this option in an airplane, and they are designed to be operated by two people.
I don't have anything against cadets per se as I had a first job once too, but maintaining a good mix of experience in your hiring policies is a wise thing to do. Even if it costs a few bucks.