His brain seems to be wired up differently: He's frustrating, he's terrible at people skills, and he'd walk 10 miles out his way to avoid bending a minor ethical principle. Even when I disagree with one of his ethical principles, I do admire him for being committed to what he believes. I suspect he could have made a very profitable business off of GCC in the 80s—it was a remarkably good compiler for several chips back in the day—but he preferred to focus on writing more free software.
I've spoken with FSF staff in the past, and their attitude towards Stallman often seems to combine admiration and frustration. They work with him regularly, and most of them are fairly typical free software developers. They generally seem to believe that world has room for somebody like Stallman, who's horrible at PR but who takes principled stands.