Diseases of the body can spread through a population and reach epidemic proportions, but so too can diseases of the mind. And of these epidemics of the latter variety, mass psychosis is the most dangerous. During a mass psychosis, madness becomes the norm in a society and delusionary beliefs spread like a contagion. But as delusions can take many forms, and as madness can manifest in countless ways, the specific manner in which a mass psychosis unfolds will differ based on the historical and cultural context of the infected society. In the past, mass psychoses have led to witch hunts, genocides and even dancing manias, but in the modern era it is the mass psychosis of totalitarianism that is the greatest threat:
Source: The Manufacturing of a Mass Psychosis – Can Sanity Return to an Insane World?
Healing our America 