Narkissos: I very much agree that monotheism is not a necessary stepping stone between polytheism and atheism. That's why I mentioned the underground tradition of practical if not overt atheism running parallel to philosophical monotheism in the Greek world. And we can suspect that "atheism" was not unthought of in the Jewish sphere either. The motto "there is no god" ascribed to the "fool" in Psalms may well express (as well as try to repress) a very serious question, which most Bible commentaries (taking for granted that "atheism" was unthinkable to the Ancients) explain away by making it a purely practical or moral stance.
Having long admired your thoughtful and informed posts, I didn't really suppose you were suggesting some sort of historical necessity to the ordering. My comments to that end were more of a preface.
Even as historical descriptions, though, I think the succession you propose is muddied by Catholicism having arguably moved in some important ways away from a tightly formatted monotheistic structure, which would seem to imply a retrograde historical sequencing, prior to the Enlightenment. (Although this is somewhat mitigated by the fact that most post-Enlightenment atheism was the product of regions with strong Protestant populations-- again, the tendency to iconoclasm.)
More importantly, I question whether the genuine intellectual premise of modern atheism has any more connection to a-, mono-, or polytheistic notions of the ancients than modern neuroscience does to Aristotle's take on the function of the brain, and therefore whether there is any justifiable sequence there at all. Not that there is not some sympathy and genesis in ideation between ancient ideas and modern, but that they are, at heart, more different in their foundations than they are alike.
It's been a long while, but I believe that it's in the first chapter of The Blind Watchmaker that Dawkins offers his argument that there wasn't a genuinely rational, evidentiary case for atheism prior to Darwin, a position I favor. The ideas expressed (and, very good, repressed) prior to Darwin are developmentally interesting to the growth of Western individualist thought, and, although tending towards reason and away from the supernatural, in point of testable fact, these epistemological and metaphysical atheistic claims rested on no more than a philosophical preference-- the same as theistic claims. (Unlike the heterodox or skeptically analytical materialist readings of Christianity and its tenets, which informed atheistic rationale, but are not a basis for a logical rejection of any creator, per se.)
I would therefore suggest for discussion that modern atheism has its underpinnings in the revolution in Western views of evidentiary, materialist science, rather than any ancient knowledge, or counter-knowledge. I also suggest that the philosophical roots of this Western science might be arguably traced to the dualistic iconoclasm that came up through the Abrahamic traditions.
I'd very much welcome comments on this topic from a theistic standpoint.
I think the modern theistic position is laid out ably here...
John Dryden, Religio laici, or, A laymans faith...
Thus man by his own strength to Heaven would soar:
And would not be oblig'd to God for more.
Vain, wretched creature, how art thou misled
To think thy wit these god-like notions bred!
These truths are not the product of thy mind,
But dropt from Heaven, and of a nobler kind.
Reveal'd religion first inform'd thy sight,
And reason saw not, till faith sprung the light.
Hence all thy natural worship takes the source:
'Tis revelation what thou think'st discourse.
Else how com'st thou to see these truths so clear,
Which so obscure to heathens did appear?
Not Plato these, nor Aristotle found:
Nor he whose wisdom oracles renown'd.
Hast thou a wit so deep, or so sublime,
Or canst thou lower dive, or higher climb?
Canst thou, by reason, more of God-head know
Than Plutarch, Seneca, or Cicero?
Those giant wits, in happier ages born,
(When arms, and arts did Greece and Rome adorn)
Knew no such system; no such piles could raise
Of natural worship, built on pray'r and praise,
To one sole God.
...
unfortunately, it's from 1682.
[Notice that in this snippet Dryden is actually arguing against the Deists, but I think it still works.]