All Christians are Atheists
Michael Buckley begins his monumental study of the Origins of Atheism with the simple (but often overlooked) assertion that atheism is 'parasitic' upon theism:
an inquiry into the origins of atheism must trace the intellectual process from god affirmed to god denied. The content of one constitutes the content and explanation of the other... Atheism is necessarily dependent upon theism for its vocabulary, its meanings, and its embodiments (p. 17).
Atheism is thus not a single phenomenon - it takes its meaning from the form of theism denied.
All Christians are therefore atheists: they deny certain gods. For example, as followers of the Way of Christ the Resurrected Victim, all gods of power without compassion are denied ultimate existence.
(This might well mean, for instance in a political working out of this, that Christians would reject ascribing worth to [i.e. 'worshipping'] nuclear weapons, a form of exercising warfare that inevitably cannot distinguish combantants from civilians).
Atheism is therefore central to Christian theology. Thinking about God not only involves saying 'yes' to some things that the concept 'God' might cover, but also 'no' to other things.
To put it flippantly, on meeting an atheist a Christian should well be able to respond, 'me, too! Which gods don't you believe in?'.
Or, less flippantly, the Christian may well learn from the atheist. For the Christian might - in respectful dialogue - discover that some things which s/he considered true about God may actually turn out to be morally abhorrent or intellectually confused.
Ironically, in that case, the atheist becomes a channel for divine revelation, an other 'Mary' through whom the Word, yet again, takes flesh...