After thinking about this a bit more, I think it's pretty clear that integrating a limited-access forum for sensitive issues into the LW site structure would be a bad idea; it's security through obscurity, not doing much to dissociate controversial opinions from LW in the eyes of the public or the media and almost certainly not secure against anyone determined to dig up such opinions. A less focused forum with the same access restrictions might actually be a better idea: it looks less like we're running a secret society and more like we want to keep our public-facing image on message. Private social forums are quite common on large websites.

That has its own problems, though, starting with the fact that we already have a Discussion section that does its job quite well, and that privatizing it would complicate outreach: a lot of people make their first posts on Discussion. A private mailing list run by people unaffiliated with SingInst or the LW administration might have most of the desired qualities, though; it could be kept low-key with little effort, pseudonymy relative to LW is easy to set up, discussions would be persistent, and high-karma posters on LW can say conversations are appropriate for the list without necessarily appearing to endorse its content.

Which is about what the first people to bring it up were thinking, but it's nice to have some explicit reasoning behind it.