There are two ways to read this sentence Affect meaning “To change” —> “We cannot change the ignorance (in general, of society, ...) about this matter” Affect meaning “To pretend to have a feeling” ___> “We cannot pretend to be ignorant about this matter” You will have to look at the surrounding context to determine this, but the second meaning of affect is relatively uncommon and almost never used in informal settings.

It means we can't change or make a difference to people's ignorance or stupidity on this matter/topic/belief.