One aspect of the atheist argument against religion does not hold for the very simple reason that according to the atheist's worldview, religion is the legitimate result of natural selection. Adaptation being a law of nature would make adaptiveness essentially self-justifying. According to the atheist's worldview, religion can and does exist merely because it is an adaptive trait, rendering religion justified on adaptive grounds alone.
There is therefore no truly reasonable ground for the atheist on his own terms to debate the religionist, because the religionist is simply operating according to historically adaptive traits, i.e. consistently reproducing religionists. Neither from logic nor illogic, religion according to the atheist is the result of natural selection, of genetic and social Darwinism. There can be no blaming of religion in this case, for it is simply a competing complex of traits that proved adaptive. Thus whether religion is true or false can be of only secondary importance to the atheist, for the fact that religion exists and reproduces means it obeys Darwinian natural law and so does not need to answer to any additional bar of truth in order to justify its existence.
The atheist, on the other hand, is simply some other complex of naturalistic traits, traits he would like to believe are more adaptive simply due to the complex of factors to which he is enthralled. But whether or not atheism is adaptive is not determined through argument or rational discourse, but through reproduction. In reality, atheism may be utterly unadaptive and unsustainable, a fact which history would seem to corroborate. Even so, atheism according to its own consequences is not a matter of rational discourse, nor are any beliefs. Reproductive realism, which is to say the actuality of instances of reproduction, is the only relevant law. The atheist's argument is thus anticlimactically emptied of its force because ultimately even his beliefs are only passively retained due to social and genetic Darwinian determinism, and only the presence or absence of reproduction can in principle decide the case.
If freedom of belief, however, is granted over and against reproductive determinism (i.e. those who reproduce determine the case), then again the atheist fails because the religionist according to atheist belief must then also be equally free, belief no longer being about truth but about free competition for existence, truth again being relegated to secondary importance.
But if the argument is about truth, where atheism considers itself more adaptive because it is true, then the atheist would again have to betray his own worldview because truth would have to be shown to be an adaptive trait he uniquely possesses over against non-atheism. This would beg the question since it assumes the possession of the very thing in question, becoming "true" merely because he asserts it.
Moreover, if an atheist has truth as an adaptive trait, it would be in principle impossible to show non-atheists since they lack this trait, destroying rational discourse since only the atheist could rightly be said to reason. The ability to know truth is here reduced to a product of social and genetic Darwinism, and so if this is the case it again destroys the atheist's argument because his truth becomes merely the resulting consequence of his accidental traits, and thus not a function of truth. The knowledge of truth is just an accident of nature.
Worse, if knowledge of truth is merely the benefit of Darwinian adaptation, then it would never in principle be able to be known as truth because Darwinian adaptation equally produced falsehood (i.e. religion). Thus, absurdly, only the presence of atheism could demonstrate possession of truth, reducing atheist truth claims to rank tautology.