Imagine the following conversation;
Person A: I believe in ghosts, there must be something beyond the natural realm.
Person B: Personally, I don't believe in the existence of ghosts, there's no evidence whatsoever.
Person A: Oh, so you're an aghostist?
Person B: Yes
This is self-evidently stupid.
Shouldn't you only need terms for individuals who believe something, rather than a negated form for people who do not accept it? Placing the word in the negative ('a-theist') seems to imply a loss for not believing, or that it's a norm to believe. If it's needless for the supernatural ghost, then why not for the supernatural god?
Wouldn't it just be suitable to say you do not believe in X rather than attaching a label? A label also implies a certain group of values, but given that people who don't believe in god don't have this, then surely having a label is superfluous.