"Ignorant" derives from the Latin ignorantia, from the verb ignorare, to not know. (The Dutch translation is "onwetend", literally, "un-knowing"). If I had not been informed of the negative connotations it carries in English, I would have thought it a perfectly polite word to use.

People like to be able to dismiss any criticism as "calling names", "ad hominem". It is therefore unlikely that you'll be able to find a term that captures the original meaning of (wilful) ignorance without the insulting connotations. If an alternative term were to find widespread use, people would just start taking offence at the new term - being offended allows them to ignore your criticism.