Atheism is not believing, theism is believing.
Agnosticism is not knowing, gnosticism is knowing.
You can be an agnostic atheist.
My point being, being an atheist doesn't stop you from thinking about whether there is a God or not. Nor does it stop you from saying "I'm just not sure, how could I know?" You simply just don't believe in one, because the entire idea doesn't seem to 'fit for you'. The idea that an atheist can't question themselves and must remain resolute in their stance is ridiculous at best... for a lot of atheists it's thanks to that critical thinking that they were "converted" in the first place. All atheists are "true" atheists... and to suggest otherwise suggests a real lack of understanding about what atheism is--and only goes to further distort what this discussion could potentially be... but maybe I expect too much of the internet, now-a-days!