Perhaps they do not believe it is utterly nonsense. I don't think it's nonsensical and I read the original-source thread before any of the follow-up reporting came out about it to potentially bias my opinion (beyond my bias of "Stallman is a creep" that I've known about second- and third-hand for a decade). His behavior was appalling: the attempt to construct a situation wherein someone Stallman knew personally happened to have clean hands while hanging out with a known pedophile and sex-trafficker of children, and then judging a protest through that lens, is just not okay, and even if he didn't have a history of gross behavior--which he does--I'd have had to have a real good reason not to eject him at speed from any business or institution over which I had authority for that alone. That it wasn't an isolated incident, and was known to not be isolated before this happened (more on that in a sec), would likely only harden my resolve to show him the door.
While it was known to not be isolated beforehand, it's pretty clear to me that a number of people have felt safe to tell their own stories in the couple days since this broke. I live near MIT but did not attend, and so I am not in any particularly privileged circles; despite that, this incident prompted a lot of people to speak up about RMS's consistent bad personal behavior as well as his bad public behavior. These sorts of things have a way of providing courage to people who have felt suppressed--someone is brave enough to kick one rock and dozens more come with. I would submit that if a nobody like me is hearing that stuff it is a near-certainty that people with hire-and-fire authority at MIT, and in decision-making roles at the FSF and GNOME, are hearing it and likely more.
This is what makes most of the protestations in this thread (not, I stress, the ones that you're laying out) so disheartening. On one hand you've got people adjusting their pince-nez and going "well, really, don't we need to have a conversation about statutory rape?" (we don't), while you've got another contingent who are all about clapping for pedophiles to "own the libs". It's just...really gross, and it's not about "free thinking" or "free speech" at all. (And it never really is.)