There are speech rights that are not protected legally, rather based on culture, tradition, and so on. I don’t know what these are like at MIT, but they are fairly broad in a lot of western educational institutions.
Those aren't "rights", those are "norms." When you engage in exceptional behavior (like suggesting a child sex slave's docile appearance excuses Minksy'd responsibility to not rape kids) then your norms may find themselves superceded.
But ultimately RMS's positon was one of political, not technical, leadership. With no more supporters, the FSF rejected him. Without the FSF, what purpose could he serve at his job?
His expertise is software development and the open source world. he can make contributions as long as he is able to swing a patch against a git repository.
That doesn't imply any institution of higher learning or software advocacy organization needs to grant him their imprimatur to do it.
RMS hasn’t had a paid job as a programmer for 40 years as far as I know. People say he was homeless and living in his office at MIT while working on GNU in the 80s.
Isn’t he basically a speaker and advocate nowadays? That career is unlikely to be very successful now that all major organizations dumped him and he has fake news headlines saying he defended Epstein following him everywhere (backed up by apparently two decades of known antisocial personal behavior).
He doesn’t exactly sound like the kind of person you’d hire to work as a normal developer nor would that comport with his strange ethics of refusing to use any non-Free software.
He was in a leadership position for a long time while also having very poor soft skills. His value was primarily symbolic, and that symbolism has been pretty much destroyed at this point.
He could try to rebuild his career, but he is 66 so unlikely he will try.