Certainly not absolving the players of all responsibility, but let's be serious, they enter the league around 22, have a massive ammount of money thrown at them, and then you want them to consider their health at 40 over their next paycheck? They have some blame yes, but that's pretty clear exploitation.
And quiet honestly: the decision shouldn't be made by the players. It should be made by doctors, and it shouldn't be made on the sidelines.
Trust me, I went to medical school, the league is beautifully skewing things in their favor. For starters, they do the test on the sideline of an NFL STADIUM, its the opposite of "ideal conditions", considering you are looking for auditory and visual responses from a player who is surrounded by thousands of screaming people. Do it in the locker room.
Second, the NFL uses the SCAT-2 test for concussions: a test designed for major head trauma from car accidents, not sports injuries. It's more similar to a DUI test. If a player is able to blink on his own, he is able to pass about 1/5 of the test. A players with a sports concussion could easily pass this test. Want a good article on it? here you go:
Why the NFL Sucks at Testing for Concussions | Playbook | Wired.com
Non-guaranteed contracts: Teams have the ability to cut a concussion risk at any time. Tell me how that isn't an incentive to not have a concussion?
Lastly - and this is my key point that cannot be argued with - we can't judge the NFL because they won't release concussion statistics. Until they do, we have to assume the worst. You don't hide improvements, you hide shortcomings.