People apparently enjoy watching boxers get injured and knocked out, just as NASCAR fans enjoy seeing horrible crashes. I agree that bare knuckle fights were worse, but there is probably no way to make a blood sport less bloody without reducing its appeal to those who enjoy watching it.
I find it impossible to watch. I find boxing movies, where I know no one is really hurt that much, to be boring. And I really cannot being myself to give a damn who wins, just as in pro sports.