Where in the WBC's charter does it guarantee the right to free speech...? And this guy was Australian, not American, so how the American constitution is supposed to protect him, I don't know. The Australian constitution, based on my brief drunken review of it, doesn't guarantee any such thing. It's mostly a rant about how the Queen is a w****.
Kagy's completely right. It's not even an issue of government. A similar incident would be John Rocker's suspension. The WBA can't tell him what to say, but they don't have to let him represent them if he takes a stance they disapprove of that is amplified due to his status as a boxer.
Human beings, regardless of where they live, should be allowed the right to free speech. I don't know any other way but to say what I want, when I want, how I want, about whoever I want. Yada, yada, I know he's not an American. It's just different to see someone penalized like that for saying some stupid things. So my comment, "So much for free speech," is just a reminder of how precious our free speech is.