When they ask why he got injured you tell them it was because of his choices not yours. Injuries take from your bottom line when they result in workman's comp, which he would be denied if it was found out he was continuing to do what he was doing against the better judgment of everyone around him.

You turned an employee against you, which means you hurt the bottom line yourself, because now you'll have an employee who doesn't care, or is now actively looking for work elsewhere. In your shit attempt at being "proactive" you hurt yourself, and your team.

You could've even convinced him by being like "hey you work hard, I want to give you an easier task as a reward for that hard work". I'm sorry but you handled the situation like shit, and you come here looking for validation, you're not going to find it from strangers who are brutally honest.