Not arbitrarily. I'm believing the science that says CTE is in the family of influences that include Alzheimers and dementia, in that physical changes to portions of the brain are highly correlated with behavioral changes. You know, from doctors and stuff. I'm also not sure what the "100%" is supposed to imply, because I"m not waving my hand and absolving Nobis (or Seau, or others) of their behavior, I'm just acknowledging that there are a set of inputs involved in their decision making beyond just "self control." There's an analogy here to alcoholism, bi-polar disorder, ADHD, etc - they're still all making choices (to drive, to fidget, etc) but science has proven that there are other inputs in their brains that make their decision making more difficult, and there are treatments for those situations that vastly improve their quality of life. In the case of CTE, that treatment is "maybe don't play football ..." which is something we have to seriously consider as rational adults.
Very honestly, I can't see your angle here. What are you actually arguing? That the game is safe? That the data doesn't show that repeated head injuries cause behavioral changes? (forget "CTE" as a target ... people with multiple concussions very consistently report changes in mood, behavior, emotional regulation, and more than just football. Soccer players are apparently VERY affected).