csail-related really wasn't all that private. Anybody at MIT could add themselves to it (and perhaps could add others to it) and many undergraduates did just to see Stallman make the comments he did. (Long before this scandal, he had several amusing habits and mannerisms on this particular list.) It wasn't exactly public, but it wasn't really private either. And there had been prior scandals from it that had been made public ("a mailing list" in this article but I remember it happening on csail-related): https://thetech.com/2017/04/20/egg-donor-advert