So could it be that the problem is not stuttering, but selective stuttering? This sounds very similar to selective mutism. I think what Ciductive was getting at, was that if stutterers can speak fluently on their own, couldn't they theoretically do that with other people to? Couldn't they just shut off all the circuits of their brain that recognizes facial expressions from other people, time anxiety, fear of judgment, and just disconnect from all that? By disconnecting from all that, talking in front of other people becomes no different from talking by yourself.