why dont the existing drivers say "We aren't willing to fly with anyone who has gone through the cadets program as they are unsafe to fly with".
You may be in for a shock. Whilst it's illegal to refuse to fly with a cadet- as others have pointed out- it's very legal to stand one down if they show themselves not up to the required standard. My understanding is that just this thing has occurred in J* recently.
So now you owe a huge training debt and aren't even being paid the pittance you were 'happy' to accept. You'd better hope you're an ace and don't find yourself in that situation.