If he actually has Social Anxiety Disorder, which it appears he does from the article, then I think Dana White would be wrong and inconsiderate to cut him from the UFC.
Mental illness is just as legitimate as any other illness and should be treated as such, and it would make sense that Diaz would have debilitating anxiety when he has to give the biggest press conference for the biggest fight against the biggest fighter of his LIFE.
I'm sure some people are thinking "well if he's so anxious then how does he get in a cage and fight" but fighting is not a social activity and as such it has no significant relevance to social anxiety disorder. In fact, one could argue that fighting is inherently an ANTI-social activity.
Furthermore, this isn't the first time we've seen something like this. Old NFL fans like myself will tell you that Ricky Williams also had social anxiety disorder; he would give interviews and press conferences with his helmet on because he would get so afraid of talking but that didnt stop him from being a monster on the field. Unfortunately, like Diaz, his anxiety hurt his career by leading him to retire prematurely (and temporarily) from football and also "self-medicate" with constant marijuana usage.