I have to agree with Dan here. (I'll wait a moment for everyone to stop gasping... ) Football players are not like baseball players with guaranteed salaries. They're tossed on the scrap heap at a moments notice, contract cancelled. As far as "knowing the risks beforehand", get real. People don't just decide to start playing football at age 21 and go pro. This is absurd. Childhood dreams are formed in childhood, and if you're actually dedicated enough to make it to the pros (or even a major college program), its hardly likely that you made a concious decision as an adult to play football.
Dementia isn't the only problem facing explayers. The physical damage is just as bad. So many former players can barely walk, due to arthritic knees. And if you really want a scare, look into the difference in life expectancy between NFL players and the general population.
I won't jump on the "ban the game" bandwagon just yet, but if anyone out there thinks boxing should be banned and football is okay, well, I have to question your command of logic...