Another thought occurs to me regarding something you may need to talk to him about. If he doesnt learn to deal with this now - at some point in his life he is going to have a much bigger problem to deal with. Debt never gets smaller unless you work at it.
So many people are literally crippled with fear at the size of thier debts. They cant sleep, they cant function ands they spiral down in to a very black pit. Hopefully - the size of teh problem now is not too big a task to deal with. If he ignors it (even if he succesfully runs away from it) whats to stop him getting into debt again???? He'll be just as likely to mess up again as soon as he gets a new credit card.
If he does it now, hopefully in his thirties (if he can think that far ahead) he wont be in such a pickle as lots of people are. And maybe - juts maybe - he will be one of the few people who understand that a credit card does not mean the bank is giving you free money to spend. Its not a gift out of the kindness of thier hearts - and they WILL want it back.