What they did will fracture the community anyway. You can bet there are Stallman supporters in GNU, too. If the undersigned have it their way, others will leave (or disengage), in protest. There's no winning in this. From my pov, what they did has only downsides, and no upsides whatsoever.
You don't like GNU? Fork their software, make your own GNU with vodka and hookers. Just, don't throw a public tantrum. Use official channels and due process. If the organization doesn't respond, and doesn't match your values - just leave.
Stallman created that movement and has a lot of community support. Outing him to the public without discussing in private or even giving something actionable is just inviting outrage.
If you disagree with an organization, quitting and/or forking (and announcing your reasons) is less damaging to the cause than this.
Either way, I think a lot of it is social posturing, as part of individual distancing from the transpired scandal. E.g. some of the friends/relatives of the signatories now view RMS strictly negatively, so they try their best to distance themselves (or, interpreting charitably, the corresponding GNU subprojects) to try to salvage some reputation.
Note that the Joint Statement does not take a position on the statements that the most recent controversy has been about. Instead, it speaks about "behavior over the years"[0]. Of course, the recent controversy doubtless played a role in bringing all this to a head, but it is possible for someone to believe both that RMS is "completely innocent" of wrongful conduct and that he has engaged in behavior that harms the cause of Free Software.
[0]: > Yet, we must also acknowledge that Stallman’s behavior over the years has undermined a core value of the GNU project: the empowerment of all computer users.