I think this is unfair. Stallman is seen this way, I think, because of his appearance. If he cut his hair and wore a suit, he would be the Ralph Nader of software.
If you watch his interviews, he is very calm, precise, and careful to explain his ideas.
Maybe I'm radical, but he seems a very reasonable person to me.
I think that, on the whole, his eccentricity and out-there image has helped his cause and not hurt it. He's far more instantly-relatable to both geeks and normal people, whereas someone like Bruce Schneier really only relates to geeks.