Banishment is to merciful. Instead a prince is stripped down to a soldier, an easy disposable to be set in the middle of a war. To be treated like a new recruit at 13 when the rest are 16, working harder to just survive for his country. No longer a prince. No longer the son of the fire lord. He'd be less than dirt on enemy grounds, surly to be left behind like the soldiers he defended before he was permanently reminded of his mistakes. A child soldier that won't last two months, weak and slow is what will get him killed. Three weeks until his slow death. To never return home or given a chance to redeem himself. He would never restore his honor.