In neither case would I be confident that the bad PR they've avoided by hiding embarrassing things hasn't been worse than the bad PR they've abetted by obviously dissembling and/or by increasing the suspicion that they're hiding even worse things.

Exactly. That's why I'm not actually advocating any of these technical solutions, just pointing out that they do exist in solution-space.

The solution that I'm actually advocating is even simpler still: do nothing. Rely on self-policing and the "don't be an asshole" principle, and in the event that that fails (which it hasn't yet), then counter bad speech with more speech: clearly state "LW/SIAI does not endorse this suggestion, and renounces the use of violence." If people out there still insist on slandering SIAI by association to something some random guy on LW said, then fuck em - haters gonna hate.