You might argue that insiders are dangerous. They’re dangerous because they’re authorized to do things, and so monitoring throws up a great many false positives, and raises privacy concerns. (As if anyone cared about those.) And everyone in information security loves to point to insiders as the ultimate threat.
I’m tempted to claim this as a nail in the coffin for the insider as the most important threat vector, but of late, I’ve decided that the insider is an near-unkillable boogeyman, and so ‘nails in the coffin’ is the wrong metaphor. Really, this just indicates that references to insiders are a best practice, and we can’t kill them. We can, however, treat those references as an indicator that the person speaking is probably not an empiricist, and discount appropriately.