My only point is that this particular "John Carlson Lecture" is itself a public relations event whose purpose is to promote MIT to the local public and enhance its image, they allude to this in the official statement [1].
In my opinion, a PR lecture cancellation is different from telling a student group or department that they are not allow to invite a specific speaker: it is bad, but much less dangerous to academic discourse than previous cancellations (even if in past examples the speakers mentioned in the article had extreme or bizarre views).
[1] https://orgchart.mit.edu/node/6/letters_to_community/importa...
First of all, who says? Second of all, just because a majority believes something doesn't make it right. There was a time when the majority of Americans believed slavery was OK. Times change.
EDIT: the other point that the article makes is that this professor's "controversial" views are held by upwards of 70% of the American public. The net result of applying this rule consistently would be that a strong majority of the American public cannot express their opinions on this subject because of a tiny vocal minority.