"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.
In French "ignorant" just means "not knowing", and though it has a connotation of being generally uneducated and possibly stupid telling someone they're ignorant in the context of a particular topic usually goes over well. The connotations in English are much more negative, and I got seriously bitten in the ass over that.
Edit :Excellent suggestions in the comments. Two of them stood out for me:
We often use "insane" to describe people whose behaviour or beliefs are below the sanity waterline. But as most must would agree here, you cannot call someone insane with a straight face just because he happens to believe in magic.
I'm currently watching Future by Design, a documentary featuring Jacque Fresco and the Venus Project. Jacque came up with this word, "unsane", to describe people who basically, aren't rational because they haven't been exposed to the right ideas yet. Which would be different from "insane", which is more about irrevocably irrational people.
I like this word, because there isn't the tone of accusation we find in "insane". This neutrality makes it easier to say that we can do something about it. Insanity should be eradicated like vermin. Unsanty on the other hand can be fixed.
So, do you think this word, "Unsanity" might be worth using?