Willful ignorance is nearly as difficult to fix as stupid.
I think it's much more difficult. Educators can always identify and work with that "lowest common denominator." No matter how far down they might happen to be, one can always bring them up a notch or three.
The willfully ignorant, however, are like mental moles. The moment they detect anyone or anything bringing them up to the light of day, they start digging, and hard.