An evolutionary debunking argument against theism can be employed defensively or offensively by an atheist. Applied defensively, it is a response to the theist’s offering an argument from the prevalence of belief in God. Applied offensively, it is suppose to show that whether or not God exists, because theistic beliefs come from a suspect source, they are not knowledge.
The focus of debunking argument tends to be on mimetic selection. The idea is that theistic (or maybe more generally supernaturalistic) beliefs confer some kind of a selective advantage on the communities or individuals exhibiting them, and hence we can explain naturalistically the prevalence of these beliefs. This explanation works whether or not God exists, and hence whether or not God exists, typical theists’ beliefs are not knowledge.
But there is a serious gap in this argument. Mimetic selection only operates on a belief once the belief is in place. But we still have to ask: Where did the belief come from in the first place? And I think that if we are to be honest, we have to say that not only is this something we don’t empirically know, but given how it concerns fine-grained details of events before written history, we have no empirical access to the answer. For any particular lineage of theistic beliefs, there was a first believer in the lineage. How did they come to believe? Well, we can make up a bunch of ideas:
They were philosophically inclined and came up with a good argument for theism (say, a good design argument).
They were philosophically inclined and came up with a bad argument for theism (say, a bad ontological argument).
They got an apparent perception of God from eating bad mushrooms.
They got an apparent perception of God from God.
They were bullied into believing in God by a tribal leader who claimed divine right of ruling.
They heard a fairy tale told by their parents and misunderstand it as history rather than fiction.
And a lot more. The point is that empirically we have no idea. And it may be that for different mimetic lineages the initial explanation is different.
Now notice that the options include ones that are friendly to theistic knowledge (1 and 4) as well as ones that are unfriendly (the others). Furthermore, if the lineage begins with one of the options friendly to theistic knowledge, then we might say that this knowledge was then testimonially transmitted. Of course, the selective facts helped with the transmission. But as long as the chain of testimony goes back to a case of genuine knowledge, the fact that the transmission was made possible by selective effects that are not as such truth conducive may not undercut the possibility that the chain actually does transmit knowledge.
I think this line of thought is most plausible if you have an irreducible view of testimonial evidence.