I agree that there is some sadism involved in boxing (and in any other sport of such nature), but I think that the enjoyment of the contestants lie mostly in their own performance in the ring and winning a fight and less on hurting their opponents. Secondly, I think that the barbarity of the game is much more limited and controlled unlike gladiatorial fights because there are many rules to follow, there is a certain number of rounds, there is a referee (who may stop the fight if he thinks that a boxer is not capable of taking further blows), and the opponents are never supposed to intentionally kill each other.
Boxers are already trained to get hit in the face, getting hurt, punched, and all that stuff. So, they don't really care about the physical pain as much as they do as the (psychological) pain of losing.
Boxers are already trained to get hit in the face, getting hurt, punched, and all that stuff. So, they don't really care about the physical pain as much as they do as the (psychological) pain of losing.