Shouldn't a lack of belief in god imply
No. Why would it?
"I don't know" is a perfectly valid answer. Sometimes it's called Knightian uncertainty or Rumsfeldian "unknown unknowns".
I agree that "I don't know" is a better answer as there is no reason to talk in rational jargon in a case like this. Especially when we haven't even defined our terms. But could you explain to me why assigning 0.5 probabilities in the two opposites (assuming the question is clear and binary) does not make sense for expressing ignorance?
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.