I don't disagree with your intent, but definitions matter. It is through using words as they are defined (even if only in the vernacular, as long as the target audience understands) that we are able to effectively communicate. In your case you are telling them a direct lie (you are saying "the definition of ignorance is not the definition of ignorance") and then implying your new definition. This immediately discredits your argument for anyone who knows the definition.

If your intent is to convey your meaning without alienation you could instead say:

"You are not foolish for not knowing, you are willfully ignorant for not wanting to know."

Though in truth, I see no problem with replacing the willfully ignorant with foolish either.

"You are not foolish for not knowing the truth, you are foolish if you don't want to know."

This is not CALLING someone foolish (which would be offensive), this is giving them an out from the trap of foolish behavior (an enticement to join the smart people).

I don't disagree with your intent, but definitions matter. It is through using words as they are defined (even if only in the vernacular, as long as the target audience understands) that we are able to effectively communicate. In your case you are telling them a direct lie (you are saying "the definition of ignorance is not the definition of ignorance") and then telling them your new definition. This immediately discredits your argument for anyone who knows the definition.

If your intent is to convey your meaning without alienation you could instead say:

"You are not foolish for not knowing, you are willfully ignorant for not wanting to know."

Though in truth, I see no problem with replacing the willfully ignorant with foolish either.

"You are not foolish for not knowing the truth, you are foolish if you don't want to know."

This is not CALLING someone foolish (which would be offensive), this is giving them an out from the trap of foolish behavior (an enticement to join the smart people).