Brain damage at birth. A fundamental defect from birth. Not kidding either... it has to be a mental condition.
I see a couple of factors. First, the ever more extreme level of indoctrination in what passes for an education system. Second, a propensity, created by nature and/or nurture, to absorb, retain, and believe said indoctrination. Honestly, I believe it to be much like certain people have a serious propensity for various addictions. I believe the indoctrination, much like a drug, alcohol, sex, hoarding, etc, takes the place of, or fills the hole, that is either genetic or environmental.