TLDR: the accusation of harassment is 100% determined by the accuser. The determination of whether harassment occurred OTOH is decided by HR after judging the merits (or lack thereof) of the case.
I see no reason why MIT shouldn't have proceeded similarly. And while you might argue that's not 100% impartial, that's a lot better than a Twitter mob (to me at least).
Given the piles of video and text of Stallman being Stallman, and the "Hot Ladies" bit on his office door, do you really think they would have high-fived his conduct and told him to carry on? I'm cynical, but I'm not that cynical.
Or let's put this another way. The Unabomber and Charles Manson got their due process. Are you saying Stallman is worse than both of them? So I'm guessing you guys downvoting me no longer believe in our legal system? That'll end well I'm sure.