Perhaps "pathology" is too strong a word... But to your point, meeting someone isn't the same as knowing them. Did you get the chance to discuss, say, why the GPL license was too "contagious?" Let me say again I've neither met nor gotten to know Stallman, but let me share my experiences with this personality type, just for future reference.
I've gotten to know a few people who have the type of personality I describe. In particular, I have the infrequent occasion to enjoy the company of someone who also charming, funny, intelligent- all of the things that make for a great lunch or evening. However, you'll never change his mind about anything. When he makes up his mind he is absolutely convinced he is right and there is nothing he has overlooked.
And sometimes he just doesn't know what the fuck he's talking about. He'll talk about how his doctor is full of shit because what the doctor said doesn't fit with his mental model that he built upon reading a couple of articles in a science magazine. Or how teachers ought to do "X" (he's never taught). Or how programming is "Y" (not a programmer). Or how the football coach should do "Z" (never played or coached). Backs everything up with solid-sounding, logical arguments. But he simply doesn't know enough facts to start with the right axioms.
Very smart. Very persuasive. Very creative. And often very wrong.
Interestingly, as long as their right/wrong ratio is high, they can make great leaders- at least in the beginning of a movement. Alot of people find comfort in their black and white world.
But they are very difficult to deal with as a peer or in an employee/employer capacity. Tireless, pointless arguments that end with "I'm not convinced..." because NOTHING will convince them. They think they have the right axioms. Again, "pathology" may be too strong, but it's certainly a personality type I avoid all but the most casual relationships with if I can help it.