This is a very powerful force for human good and evil, and the main relevant difference seems to be whether one's ignorance is conscious and honestly admitted or else unconscious or denied.

If one knows one does not know, or knows one does not know everything there is to know about something, or knows that one does not know certainly and definitely and with full precision, one can use his knowledge of one's ignorance to get more and better knowledge.

If one does not know one does not know, or does not wish to know one does not know, or pretends to know where one only believes, one's ignorance is easily dressed up as faith or ideology, and is often used as a political or religious power to produce more ignorance that is dressed up as faith or ideology.

And notice that one may quite certainly know that one is ignorant about something, or indeed carefully ignore the relevant evidence and believe one knows something because one does not know and chooses to neglect, dismiss or avoid whatever is known about it.

"It ain't what a man don't know that makes him a fool, but what he does know that ain't so."
   (Josh Billings)

By contrast, recognized and admitted ignorance about something is a positive source of and reason for finding positive knowledge about it, if one can, and not to believe blindly or wishfully as long as one doesn't have such knowledge (probably).

And man may be an animal that desires to know, according to Aristotle, but most men - quite possibly all - actively desire not to know certain kinds of things, especially such as they disapprove of or disagree with.