Why is it easy to conclude that brain injuries can result in violence towards one's self (suicide), but not violence towards others (murder)?
Read up on Charles Whitman sometime - scary **** what a poorly placed tumor can do to a morally outstanding young man.
For a really good read (that yes, delves into very difficult questions of free will), try this article from the Atlantic:
The Brain on Trial
There are too many well documented cases of people's brains being altered (by trauma, tumors, medication or disease), and them engaging in violent behaviour towards themselves and others to dismiss.
Oh there's no question brains are "altered" by lesions or trauma. They absolutely are. We can all agree on that. But no one cares about what their brain looks like on MRI. Or rather, that in and of itself doesn't alter someone's life. You can have an MRI or CT with lots of atrophy (in older people, for example), but the person feels fine. Sure, you might find something if you really did rigorous psychological testing, but really, if the person feels fine and has no complaints, is it worth it?
The questions that are more important are:
To what extent are behavioral/cognitive changes able to be classified as "abnormal" compared to an otherwise similar (if not for the repeated traumas) cohort?
To what extent does MRI evidence of damage correlate with behavioral/cognitive changes?
If MRI's don't correlate with damage accumulation well enough (and I'm quite sure they wouldn't, realistically), what is a better tool to measure the clinical effects of these repeated injuries?
How much is too much? Are different people's brains more or less susceptible?
And where's the line - is every potentially harmful activity or avocation waiting in line to be shut down?
I don't know, I'm just spitballing here, but it would probably take hundreds of millions of dollars to answer all these questions, and my instinct tells me the answers would be pretty much exactly what common sense would tell you. A lot of "well, it depends", and eventual conclusions that sound a little, "yeah, duh". And who's going to pay for it? Taxpayers? Is that really a good use of tax dollars? To see how many multimillion dollar seasons Tom Brady can get in before retiring to be a well-dressed commentator on TV with a yacht and 4 houses? Or worse, Colin Kaepernick? Taxpayers ain't gonna wanna pony up for these ultra rich dudes who make 100 times what they do playing a game. Personally, I would rather the government fund research to improve treatments for potentially treatable diseases that apply to society as a whole. I mean what percentage of the population plays pro football? You could probably apply some concepts from something the government would (and should) pay to study, like military brain injuries, but is that really the same thing? Same cohort, same repeated injuries? Not really.
So who else would pay? The NFL? They're a business, they have no vested interest in pouring all their profits into looking for ways to limit their talent supply in the future. I think football will die a slower death of a thousand cuts, people publishing occasional studies (ideally funded by NFL players' philanthropic dollars themselves, which would be truly admirable, but that requires them to give up some of their money) in spite of those financial barriers and how difficult these things are to study (and how long it likely takes to follow one player through their career is what, 20 years?), the league slowly increasing the strictness of hitting rules, fans slowly getting less interested because there's so many penalties and softer play, people nervous about letting their kids take a hit wrapping them in bubble wrap, I think it'll evolve into obscurity in America because we're so, I don't know, for lack of a better word....high-strung, not because we showed conclusively that it was a problem that we identified very specifically, knew exactly what the consequences are, and acted to prevent them, and didn't infringe on personal liberties.
Interestingly, you never hear about CTE in rugby players. You also never hear about kids with peanut allergies being fed with a peanut-based nutritional substitute (which is real) in Subsaharan Africa. I leave you to think about why that might be.