Understanding is not "knowing"; it is a complex question related to "multiple-angle perception". It is the enemy of all forms of dogma and requires the capacity to constantly question and to nourish our capacity for independent thinking.

Those who do not have the ability to understand cannot understand; 

Those who do have the ability often choose not to nurture and develop it for various reasons; 

Those who do choose to try to develop this ability, rarely speak out enough, perhaps for fear of erring. 

One can see how such a state of affairs might elevate ignorance to a dangerous level of influence.