Messer Francesco,
I have done as requested and spoken with your son. I agree with your assesment, though only in part. Yes, Vieri is brash and acts without forethought. And he has a habit of treating the mercenari like playthings. I've received reports of at least three men being disfigured as a result. But I do not think him, as you put it, beyond repair. Rather, I believe the solution to a simple matter.
He seeks your approval. Your attention. These outbursts of his are a result of insecurities borne out of a sense of inadequacy. He speaks of you often and fondly expresses a desire to be closer to you. So if he is loud and foul and angry - I believe it is simply because he wants to be noticed. He wants to be loved.
Act as you see fit on the information I've given you here. But I must ask that we end this correspondence. Were he to discover the nature of our conversations, I fear what might become of me.
Yours in Confidence,
Fra Giocondo