It's all well and good stating that there's no proof Ali's Parkinsons is related to boxing, but turn and look at the many ex-boxers who can no longer string a coherent sentence together. Accumulative brain damage from combat or contact sports such as football is real and that is the issue. There's plenty of studies out there - the evidence is overwhlming.
Will it stop me loving MMA? No but I'm still very concious of how some of the fighters of today and yesterday might end up in a similar state as some boxers.