What it comes down to under Myriad's hypothetical, is the meaning of the word "false." The Digital Media Law Project's summary of California Law mentions "substantial truth" as a defense. Posters, including Myriad, have asserted that calling a sexual encounter "rape" is defamatory unless it conforms to the statutory definition of rape. Even if the encounter didn't meet the statutory definition, I don't see how a woman truthfully reporting that Shermer and she had sex in a way that made her feel violated could ever be defamation, but I don't know this area of law at all. I don't think anyone asserting otherwise does either.
Shermer, in the demand letter, has taken the position that this didn't happen at all, in which case it's clearly defamation.
I suspect, and I would find it reasonable, if the line is drawn between actions that are criminal and actions that are not. Accusing someone of having had sex with someone who later regretted it, should not be defamation. Accusing someone of rape is a very different matter, because it will likely ruin the accused's career and have severe social repercussions. That accusation had better be true, if it's made.
