Guess I'd disagree with Mr Heinlein on this point. Ignorance (in the sense of honestly lacking information) is not a sin, but stupidity is, since stupidity is ignorance which, through laziness, arrogance, fatal lack of imagination, hatred or any other attitude which prevents one from removing his head from his rectum, is willingly maintained for purposes other than conforming to what is true. Ignorant people can be filled with information, as a starving man can be filled with food; stupid people are like starving people who either reject the food given them or, consuming it, head directly for the vomitorium. Stupid people may suspect they are stupid, or they may well not know it, but even if they suspect they are, they will never admit it, as this will mean the complete reorganization of firmly-held opinions or fantasies or hatreds that are the foundations for their stupidity.
And, unfortunately, in some professions (e.g., politics, acting, advertising) it can afford some success and a very nice living which can batten the barriers between their lives and reality, allowing them decades of damage. In fact, some professions provide stupidity with a broad, clear field to work in, and reward it handsomely, allowing the stupid to do years worth of damage to the real world before that supposedly inevitable verdict is issued by the universe.
Or maybe not.
And, unfortunately, in some professions (e.g., politics, acting, advertising) it can afford some success and a very nice living which can batten the barriers between their lives and reality, allowing them decades of damage. In fact, some professions provide stupidity with a broad, clear field to work in, and reward it handsomely, allowing the stupid to do years worth of damage to the real world before that supposedly inevitable verdict is issued by the universe.
Or maybe not.
No "not" about it - you nailed it.