Ignorance can be much more than a metaphor indicating darkness of the mind--it can be the darkness of the mind. One who is ignorant refuses to believe, accept the truth, or understand their actions. Shakespeare's words can be a universal truth since ignorance is not fiction--it is something that makes up a lot of today's society.
Note: I didn't read Shakespeare, so if there are things you feel need to be included, go ahead and add it. :)
