That's not to condemn (or defend) the professor. This just isn't a fair characterization of the debate.
Edit: reading up a bit more it seems Galileo had a bit of a Linus T. streak, with gratuitous insults and ad hominems against authority. Makes me want to read the source documents now :-)
E.g. "red is a better color than blue" is obviously a subjective opinion, where as "ʻOumuamua is made of frozen nitrogen" is obviously a falsifiable statement.
"Therefore, as a junior member of the Flat Earth Society, I demand MIT provide me an auditorium and a microphone to legitimize and amplify my nonconformist opinion about the shape of the Earth."
MIT is obviously only going to consider inviting speakers that would appeal to some subset of its community. The statement doesn't give anyone a right to demand an audience at MIT, it gives the MIT community license to invite controversial speakers.
MIT isn't protecting all legal speech, they're amplifying speech the MIT community wants to hear, and suppressing speech the community doesn't want to hear.
If the MIT community wants to legitimize and amplify speech about perpetuating the current hierarchy of elites, and suppress protest speech aiming to open up and overturn that hierarchy, it's up to the community.
It has nothing to do with the First Amendment.
Contrary to all the feel-good language about platforming nonconformity, the goal is not to provide an equal platform to all viewpoints, because that would be ridiculous.
Ideas are still subject to the marketplace, and the MIT community is a very discriminating market.
Since there are infinite crackpot ideas but only one Kresge Auditorium, the MIT community must make value judgments about what speakers and ideas are worthy, and which ones are not.
No institution should be compelled to provide a platform for all speakers and ideas. Some speakers and ideas are worthy of MIT, and many are not.
MIT faculty and leadership should embrace their fiduciary duty to make these hard judgments. They should grapple with what it means for speakers and ideas to be worthy, and what speech should not receive MIT legitimacy and amplification.
Instead this statement evades all of that by pretending to support all speech as long as it's legal.
But this is the key thing: Abbot was giving a talk on environmental studies, and confirmed affirmative action was not part of the talk he was giving. The push to exclude him was on the basis of something other the science of his talk.
Here's a better analogy: would it be appropriate to cancel musician'd concert because he's a flat earther? The argument that we have only one auditorium and we should allocate it to a better musician does not make sense unless there's a compelling reason to say that his musical performance abilities are affected by a belief in a flat earth.
AIUI this was controversial, but not for the reasons you might think: people were concerned that the guy wasn't well and that encouraging him wasn't kind.