Everyone bar nobody has formed an opinion on an important topic that is completely wrong at some point in their life. To correct their opinion, they will need to talk to somebody who will explain why it is wrong.
This wasn't Stallman trying to use his position on the FSF to spread his opinions, he was using his position at MIT to try and defend a colleague to other academics. And what you are describing is an unreasonable standard to hold anyone to if a topic isn't supposed to be their central area of expertise.
It does matter what he advocates and it does matter whether his opinions are technically correct and incorrect. The 5-days-comment-to-resignation mob are doing damage here; and setting up terrifying dynamics. They aren't going to stop at Stallman.
Truth doesn't count if the thing hurts someone. Intent doesn't count if harm was caused. This is a view that many here would seem absurd but which many here would also agree with.
Does this still seem fair? Is truth and intent not that important when it comes to tricky issues?
If he said this anonymously or in private it would've been fine. The problem is him using his platform for stuff that it's not meant to be used for. So now they're taking away his platform. Seems fair to me.