A Short History of Stupidity by Stuart Jeffries review comfortably dumb?
Stupidity is a multifaceted, historically shifting concept with definitional ambiguity, encompassing ignorance, foolishness, obtuseness, and cognitive failings reframed by the Enlightenment.
One obvious problem, as noted by John Locke, is that "people can apply sounds to what ideas he thinks fit, and change them as they please." This leads to confusion.