Ever hear a child put his hands over his ears, or sometimes closing her eyes too, and chanting loudly, "I can't hear you - lalalalala"?
Aside from the old adage that "there are none so blind as those who will not see", there are different names for this concept, such as "selective ignorance" and "self-imposed ignorance". I often use another term, because I think "willful ignorance" fits better due to the fact that it takes a conscious decision to decide to stay ignorant about an issue on purpose - especially when there is so much information available.
We are surrounded by it, and so as far as I'm concerned, to remain ignorant about some things must take a supreme effort of will.