Ignorant is used in this sense also for someone who intentionally ignores. You can consider ignoramus as a noun.
The word ignorant is an adjective describing a person in the state of being unaware and is often used as an insult to describe individuals who deliberately ignore or disregard important information or facts. Ignoramus is commonly used in the US, the UK, and Ireland as a term for someone who is willfully ignorant. Ignorance is distinguished from stupidity, although both can lead to "unwise" acts.
Another term that might fit is willful, which can be used for someone who is stubbornly ignorant even he or she is aware of the consequences.
Having or showing a stubborn and determined intention to do as one wants, regardless of the consequences or effects
There are synonyms of willful like headstrong and self-willed but they are closer to stubbornness than ignorance. There seems to be a fine line between stubbornness and ignorance.
Note: The blank in your example is better filled with a noun. So in this case, ignorance or willfulness would fit.
wilfullness (n) a steadfast adherence to an opinion, purpose, or course of action in spite of reason, arguments, or persuasion
her unceasing willfulness eventually wore down her critics and opponents
Alright, if you want a strong word but not as derogatory as stupid, you can consider bullheaded for the person, and bullheadedness for the blank in your example.
bullheaded (adj) not willing to change an opinion, plan, etc. : very stubborn in a foolish or annoying way