How many players get life threatening injuries? They know the risks going in that someone may slash you and may cause carpol tunnel syndrome later. No professional sport has done away with lifelong injuries.
CFL players have to do it for a tenth of the money.
No one is suggesting that all risk be eliminated. Just head shots. Unacceptable risk. Unnecessary risk. No need for it. No need to
baby players by allowing it because you are tall. No need to
baby players by allowing it because you are careless.
Saying that people know the risks going into their occupations is no excuse for unnecessary risks. Make the rewards high enough and people will risk anything, just for the entertainment of the crowds.
We used to have bear baiting, dog fighting, cock fighting, all for entertainment. Society has outgrown such practices. They still happen but are illegal and highly disapproved of by larger society. We used to have human sacrifice and competitions where people fought to the death too. Just for entertainment. We have also outgrown those things.
We now know a lot more about the danger of head injury than we used to. Knowing makes it unacceptable.