Stallman is the guy who pushed the asteroid and watched it sail harmlessly past. In alternate reality, Gates is the guy on the ground helping the survivors clean up after the asteroid hit.
Metaphorically, of course. Stallman's good is causing unknown amounts of freedom restriction and consequent problems to not ever have happened - which isn't really tangible.
Without Stallman and the GNU, we would still have just as much software on the market. Many of the people and companies would have most likely released it under the BSD license (or public domain).
..and like I said. I still don't buy it. Piracy causes unknown amounts of damage to commercial software companies. If the community comes to terms with this, I might be more apt to come to terms with the amount of unknown "good" Stallman has done.