I've been reading these comments all day and can see both sides of the debate, but here's my problem with it.
There's an automatic assumption in the original post that Actor C doesn't deserve the job.
Actor C may not be reliable, he may not be very good, he may treat the whole job as a big joke. If that is the case, actors A and B will undoubtedly go on to have better careers - actor C will develop a bad reputation so he won't be hired for anything after a little while, or he'll give up acting when he realises it involves actual work and effort.
On the other hand, Actor C may have retired from his old job after building a credible work ethic that he then goes on to apply to his second job, he may have a natural talent that he will then spend the next 20 odd years spending his time and effort - time when most people would have stopped working altogether if he is supposed to be retired - developing so he can build a CV every bit as impressive as the other two's.
If that is the case, what right do actors A & B have to prevent him from doing so?
As for the value of drama school training, it is supposed to equip you with a set of skills that make you a better actor than joe bloggs on the street, thus improving your chances of getting a job. It gives CDs a clear indication that yes, this person has this set of skills, and it's very useful. But it's not, and it shouldn't be, an automatic entry to any job because it's not necessarily an indication of talent or reliability.
If you went to drama school, can you honestly say that every person you trained with was a greatly talented, fully committed actor?
To put it another way - Plumber A trained at college and passed his exams but he shows up three days late and your cellar is now flooded.
Plumber B did an apprenticeship, set up on his own and accidentally mixed up the hot and cold water so now your sink only runs cold and your toilet flushes hot.
Plumber C is your neighbour, he has a spanner and a love of DIY, but he showed up when he said he would, did the job you asked him to and everything works perfectly.
That's not the way it always goes, but sometimes it does. And if it does, who would you want to fix your pipes?