First of all, you have to accept that you are in no way responsible for what happens to this animal. You can only try to make its life better by giving its owner the best advise you can possibly give. If he follows it is not in your hands!
You know the way to take care of a bearded dragon and every bit of knowledge you share will make this dragons life a little better. I understand why you are frustrated, and I would be too, but don't give up on him because it is not the human that will suffer from it but the dragon!
Even if he isn't ready yet, maybe he will be soon. If not....giving a helping hand is all you can do. Without your help this bearded dragon might as well be gone already so you can ONLY help here. Nothing you say or do would be bad IMO.