In this case we basically only have one source for the statement. I don't remember seeing anyone else aside from the OSNews guy mentioning that statement.
Some other blogger tried to get a transcript of the Q&A that Stallman was giving but the FSF apparently doesn't keep transcripts of Q&As (they probably didn't record video :/)
If it's so dubious, why do the fanboys not question that remark, but immediately leap to defend it and either try to redefine "traitor" as meaning something else or declare that they agree about the supposed "treason"?
Now, to be terribly fair, it's probably true that even if he didn't say it, everybody would be acting the same way. Nobody, even his fans, really doubts that he would say it. It's his style, and it's the exact sort of obnoxious remark his fanboys are used to defending and supporting.
EDIT: Ultimately, my complaint is about the fanboys. Someone made a dickmove. That someone is an icon to the fanboys, but he hasn't actually done anything in years besides be an icon to them, so it's barely even a story before the fans get involved.
1) Some guy says something obnoxious.
2) Bystanders observe, "What a dick-move."
3) Guy complains that people are trying to censor him because they dare say that they disapprove of or disagree with him.
The main innovation in modern days is that for some folks, fanboys will take care of step 3 on behalf of the guy who's "under attack".