"Atheism" is a word used by religious people to refer to those who do not share their belief in the existence of supernatural entities or agencies. Presumably (as I can never tire of pointing out) believers in fairies would call those who do not share their views "a-fairyists", hence trying to keep the debate on fairy turf, as if it had some sensible content; as if there were something whose existence could be a subject of discussion worth the time.
People who do not believe in supernatural entities do not have a "faith" in "the non-existence of X" (where X is "fairies" or "goblins" or "gods"); what they have is a reliance on reason and observation, and a concomitant preparedness to accept the judgment of both on the principles and theories that premise their actions. The views they take about things are proportional to the evidence supporting them, and are always subject to change in the light of new or better evidence. "Faith" - specifically and precisely: the commitment to a belief in the absence of evidence supporting that belief, or even (to the greater merit of the believer) in the very teeth of evidence contrary to that belief - is a far different thing, which is why the phrase "religious thinktank" has a certain comic quality to it: for faith at its quickly-reached limit is the negation of thought.
An excerpt from the article Gotta Have Faith? by AC Grayling.