It's been a while, but I seem to recall a client intentionally turning off their monitors via device manager on their laptops as a security measure so they could work in public without the screen being seen.
I really don't know how this might happen by accident though. It requires careful effort.
Also, on Windows 7 and earlier laptops (or at least many of them) if you use the function key that toggles the monitor between displaying on the laptop, on a secondary monitor (or projector) or both at the same time it will not automatically revert to the monitor if there is no external device present. I have been at many presentations where flustered presenters cannot figure out why their laptops are suddenly not displaying anything on the screen anymore and it's because they toggled into "secondary display only" mode rather than "on both" mode. This is something that I've seen happen unintentionally, too, when someone struck the keys necessary to accomplish it.
I don't find an uninformed hatred a "principled position" that I need to respect in any way.
~ Ellen Evans, soc.motss, 11/6/2004