I agree the commissioner makes too much money, but then, I think a lot of people make too much money - including most executives at major corporations, the president and other higher ups at most universities, and a lot of other people who have a good amount of responsibility but not nearly enough to justify what they are being paid.
As for the athletes, I think they knew what they were getting into when they decided to play in the NFL. It's the same for other potentially risky jobs. Firemen realize that fighting fires is a dangerous thing and they could get injured or even die. Police officers understand they put their health and lives on the line when they do their job. People who willingly join the military should be aware they could be placed in dangerous environments where life and limb could be in peril.
If you choose to enter a job with risks, you choose to accept those risks. No one probably forced these guys to play in the NFL, the same as no one probably forced most people to be a fireman, or a cop, or a solider or marine. Of all of those I just listed, only the NFL players are making huge salaries for the most part.
Don't get me wrong. It's a terrible thing if you get injured or killed doing your job - but you chose the job and knew the risks. Don't do the job if you're worried about those risks.
It's the same reason I feel Americans do way too much to honor past and present members of the military, but that's another topic entirely.