Consider this scenario, as though it’s a movie plot, although The Matrix comes close.
A devious, intelligent and technically superior group genetically manipulate some people into a basic state whereby they can be controlled. They sell themselves as Gods by their superior capabilities and fix the DNA so that control can be affected by dogma, sound, electronic waves, mind control, propaganda, fear, media, education, food and low esteem, and more. The degree of dumbing down is such that, if asked if that process could ever take place, there is automatic denial and ridicule at the mere idea. The standard responses would be, “They wouldn’t do that” or “That can’t be right or we would have read about it in the papers or heard it on the TV”!