I call people ignorant all the time in friendly conversation. /sarcasm
I don't see how anyone can claim to know such questions, at least until such a time as real miracles become evident to all. (That is, unless and until God chooses to reveal himself.) I certainly don't know, myself, if there's a spiritual side to the universe, since it would by nature be unobservable anyway.
The distinction between two words may be of no interest to you. However, it is incorrect to say that there is no difference. That's why there are separate words for the separate cases.