In Star Trek TOS, the Medusans were so ugly that the sight of them would drive any human completely insane. Even Vulcans, with their superior minds and physiology, could only gaze upon a Medusan with the aid of a red plastic visor.
It seems like being able to drive humans, bare-eyed Vulcans, and possibly other species insane on visual contact would be a huge military advantage.
Couldn't wars be waged where species such as the Klingons attack humans by unexpectedly showing them images of the Medusans on screen, hacking their computers with images of the Medusans, etc? Wouldn't it be possible for a terrorist to attack by displaying a giant projected image of a Medusan in the downtown area of a city with millions of people?
How is it that such a potentially cheap and devastating weapon was never exploited?