Unchurched, nonbeliever, atheist. Those prefixes – un, non, a – imply an undeserved negativity. Consider "atheist." That simply means, not a theist.
To most people this is something bad. If you don't believe in an unknown, unseen god, there's something wrong with you. But there's no term for those who don't believe in unicorns or the Tooth Fairy.
Except, "those who don't believe in unicorns or the Tooth Fairy."
A commitment to understanding reality as it really is usually is viewed as a good thing. But not when it comes to belief in god. Then those who want their reality founded on facts, rather than faith, get tarred with an epithet like unbeliever.
Carl Van Doren, though, revels in that appellation. I enjoyed his essay, "Why I Am an Unbeliever," in Christopher Hitchens' "The Portable Atheist."
Here are some excerpts for your unbelieving pleasure:
Belief, being first in the field, naturally took a positive term for itself and gave a negative term to unbelief. As an unbeliever, I am therefore obliged to seem merely to dissent from the believers no matter how much more I may do. Actually I do more. What they call unbelief, I call belief.
…What I have referred to as the gift of faith I do not, to be exact, regard as a gift. I regard it, rather, as a survival from an earlier age of thinking and feeling: in short, as a form of superstition. It, and not the thing I am forced to name unbelief, seems to me negative.
It denies the reason. It denies the evidences in the case, in the sense that it insists upon introducing elements that come not from the facts as shown but from the imaginations and wishes of mortals. Unbelief does not deny the reason and it sticks as closely as it can to the evidences.
…Many believers, I am told, have the same doubts, and yet have the knack of putting their doubts to sleep and entering ardently into the communion of the faithful. The process is incomprehensible to me. So far as I understand it, such believers are moved by their desires to the extent of letting them rule not only their conduct but also their thoughts. An unbeliever's desires have, apparently, less power over his reason.
…There is no moral obligation to believe what is unbelievable any more than there is a moral obligation to do what is undoable.
…Beliefs, like tastes, may differ. The unbeliever's taste and belief are austere. In the wilderness of worlds he does not yield to the temptation to belittle the others by magnifying his own. Among the dangers of chance he does not look for safety to any watchful providence whose special concern he imagines he is.
…He builds himself up upon truth and barricades himself with it. Thus doing, he never sags into superstition, but grows steadily more robust and blithe in his courage. However many fears he may prove unable to escape, he does not multiply them in his imagination and then combat them with his wishes.
Austerity may be simplicity and not bleakness.