One category of cases where self-deception might be (evolutionarily) adaptive would be for males to be over-confident about their chances to pick up a female for a one-night stand (or, alternative, over-confident about how pleasurable that dalliance would be, and/or about how little they would be emotionally hurt by a rejection of their advances).
Suppose that in reality the potential utility to the male of the 1-night stand (if the seduction works) is twice as much as the utility loss (if rejected) and the actual chances of success are 20%; in this case the male will never make such pick-up attempts if they have exactly correct estimations. Another male who self-deceives to believe their chances are 40% will try every time -- and some of the time they'll get the 1-nighter, and some of that time they'll sire a baby and spread their genes. Thus, in such a situation, self-deceiving for over-confidence may be adaptive.
By the way, I should clarify that my total disagreement with your thesis on WW2 being single-handedly caused by A. Hitler does in no way imply disagreement with your more general thesis. In general I do believe the "until comes steam-engine-time" theory -- that many macro-scale circumstances must be present to create a favorable environment for some revolutionary change; to a lesser degree, I also do think that mostly, when the macro-environment is ripe, one of the many sparks and matches (that are going off all the time, but normally fizz out because the environment is NOT ripe) will tend to start the blaze. But there's nothing "inevitable" here: these are probabilistic, Bayesian beliefs, not "blind faith" on my part. One can look at all available detail and information about each historical situation and come to opine that this or that one follows or deviates from the theory. I just happen to think that WW2 is a particularly blatant example where the theory was followed (as Keynes could already dimly see it coming in '19, and he was NOT the only writer of the time to think that way...!); another equally blatant example is Roman history in the late Republic and early Empire -- yes, many exceptional individuals shaped the details of the events as they unfolded, but the nearly-relentless march of the colossus away from a mostly-oligarchic Republic and "inevitably" towards a progressively stronger Principate looms much larger than any of these individuals, even fabled ones like Caesar and Octavian.
But for example I'm inclined to think of more important roles for individuals in other historically famous cases -- such as Alexander, or Napoleon. The general circumstances at the time of their accessions to power were no doubt a necessary condition for their military successes, but it's far from clear to me that they were anywhere close to sufficient: e.g., without a Bonaparte, it does seem quite possible to me that the French Revolution might have played itself out, for example, into a mostly-oligarchic Republic (with occasional democratic and demagogic streaks, just like Rome's), without foreign expansionism (or, not much), without anywhere like the 20 years of continuous wars that in fact took place, and eventually settling into a "stable" state (or, as stable as anything ever is in European history;-). And I do quite fancy well-written, well-researched "alternate history" fiction, such as Turtledove's, so I'd love to read a novel about what happens in 1812 to the fledgling USA if the British are free to entirely concentrate on that war, not distracted by Napoleon's last hurrahs in their backyard, because Napoleon was never around...;-) [To revisit "what if Hitler had never been born", btw, if you also like alternate history fiction, Stephen Fry's "Making History" can be recommended;-)]
After Napoleon, France was brought back to the closest status to pre-Revolutionary that the Powers could achieve -- and ("inevitably" one might say;-) 15 years later the Ancien Regime crumbled again; however, that time it gave birth somewhat peacefully to a bourgeois-dominated constitutional monarchy (with no aggressive foreign adventures, except towards hopefully-lucrative colonies). Just like the fact that following Keynes' 1919 advice in 1947 did produce lasting peace offers some support to Keynes' original contention, so the fact that no other "strong-man" emerged to grab the reins in 1830 offers some support to the theory that there way nothing "inevitable" about a military strong man taking power in 1799 -- that, had a military and political genius not been around and greedy for power in '99, France might well have evolved along different and more peaceful lines as it later did in '30. Of course, one can argue endlessly about counterfactuals... but should have better support before trying to paint a disagreement with oneself as "absurd"!-)
BTW, in terms of human death and suffering (although definitely not in terms of "sheer evil" in modern ethical conception), the 16 years of Napoleon's power were (in proportion to the population at the time) quite comparable to, or higher than, Hitler's 12; so, switching from Hitler to Napoleon as your example would not necessarily weaken it in this sense.
"In sober historical fact", clear minds could already see in 1919 that the absurdity of the Treaty of Versailles (with its total ignorance of economic realities, and entirely fueled by hate and revenge) was preparing the next war -- each person (in both nominally winning and nominally defeated countries) being put in such unendurable situations that "he listens to whatever instruction of hope, illusion or revenge is carried to him on the air".
This was J.M. Keynes writing in 1919, when A. Hitler was working as a police spy for the Rechswehr, infiltrating a tiny party then named DAP (and only later renamed to NDA); Keynes' dire warnings had nothing specifically to do with this "irrelevant" individual, which he had no doubt never even heard about -- there were plenty of other matches ready to set fire to a tinderbox world, after all; for examle, at that time, Benito Mussolini was a much more prominent figure, a well known and controversial journalist, and had just founded the "Fasci Nazionali di Combattimento".
So your claim, that believing the European errors in 1919 made another great war extremely likely, "is an unreasonable belief", is absurd. You weaken your interesting general argument by trying to support it with such tripe; "inevitable" is always an overbid, but to opine that the situation in 1919 made another great war all too likely within a generation, quite independently of what individuals would be leading the various countries involved, is perfectly reasonable.
Keynes's strong and lucid prose could not make a difference in 1919 (even though his book was a best-seller and may have influenced British and American policies, France was too dead-set in its hate and thirst for revenge) -- but over a quarter of a century later, his ideas prevailed: after a brief attempt to de-industrialize Germany and push it back to a pastoral state (which he had already argued against in '19), ironically shortly after Keynes' death, the Marshall Plan was passed (in rough outline, what Keynes was advocating in '19...) -- and we didn't get yet another great european war after that.
Without Hitler, but with Versailles and without any decent reconstruction plan after the Great War, another such great war WAS extremely likely -- it could have differed in uncountable details and even in strategic outline, from the events as they actually unfolded, just like the way a forest fire in dry and thick woods can unfold in many ways that differ in detail... but what exact match or spark lights the fire is in a sense a detail -- the dry and flame-prone nature of the woods makes a conflagration far too likely to avoid it by removing one specific match, or spark: there will be other sparks or matches to play a similar role.
I just find it interesting that the event is scheduled for St. Crispin's Day -- is that a reference to "we few, we happy few, we band of brothers", OR to "half a league, half a league, half a league ahead" -- or total indifference by Singularity experts on the subject of ancient battles which happened to inspire great English poets?-)
I guess that Bay Area Bayesians who are also Pythonistas are out of luck, since on Thu 21 Feb Guido van Rossum will be speaking at BayPiggies (meeting at Google in Mountain View as usual) with a much-expected talk on the status of Python 3000...:-(. Worse luck: we always meet on the 2nd Thursday of each month -- but for this one month only we moved the meeting one week later, in order to leave Valentine Day's evening free for other pursuits!-) What a difficult choice...!
If you're interested in the Blues and the Greens, check out Alan Cameron's "Cirus Factions" (Oxford University Press), a reasonably thorough monograph. There were originally two teams in chariot racing (Reds and Whites), then four (adding Blues and Greens), then six (Domitian added Purples and Golds, which faded shortly after the end of his reign), and then the Reds and Whites kinds of merged into the Blues and Greens by the 3rd century AD and those remained important for a millenium as Byzantium endured. They were handy "parties" that were often grabbed by the issue of the day (e.g., monophysites took over the Greens for a while) and eventually institutionalized as citizen militias.
If you're looking for awesome atheist poetry, Lucretius' "De Rerum Naturae" will supply it -- in Latin, that's true, but, it CAN be translated, you know;-). Yes, it DOES start with a hymn to Venus -- "hominum divomque voluptas", and the rest of the wonderful opening Hymn to Venus -- but that's just keeping the paying sponsors (the Caesars, Augustus in particular) happy, as they claim descent from Venus -- look around the "tantum religio potuet suadere malorum" part for some juicier materials;-).
There is, of course, a rather large random/unknown component in the amortized present value of the amount of good any action of mine is going to do. Maybe my little contributions to Python and other open-source projects will be of some fractional help one day to somebody writing some really important programs -- though more likely they won't. Maybe my buying and bringing food to hungry children will enhance the diet, and thus facilitate the brain development, of somebody who one day will do something really important -- though more likely it won't. Landsburg in http://www.slate.com/id/2034/ argued for assessing the expected values of one's charitable giving condiitonal on each feasible charity action, then focusing all available resources on that one action -- no matter how uncertain the assessment. However, this optimizes only for the peak of the a posteriori distribution, ignores the big issue of radical (Knightian) uncertainty, etc, etc -- so I don't really buy it (though pondering and debating these issues HAS led me to focus my charitable activities more, as have other lines of reasoning).