True, but boxers who enter this game have to be aware of the risk, and he has to accept the risk. That's why they need to have the right training so they will be 100% ready and they can take the punches from their opponent. Referee has a big role in boxing, they have to make sure that they are doing their job well to protect the boxers and to make it a clean fight.
Their conditioning is crucial and also the weigh-in is carefully checked because the overweight can throw harder punches to hurt their opponent and can be fatal as what has happened in the last decades when they don't really care about their body weight back then. Right now they are extra careful and they even cut the maximum rounds to 12 to minimize the risk of unnecessary accidents. Furthermore, the boxers are aware when their opponents are not competitive when they hurt them so much and some of them ask the referee to stop the fight.