In the main most Atheists I've met havent been very happy or well adjusted people. Some of them have been mirror images of their evangelical opposites.
For me some sort of deep down similarity in character structure explains this and also why some individuals can and do "switch camps" as they do, often with reinvigorated adamency or vigor.
However I wonder if there is any kind of correlation between optimism and pessimism and atheism, what do you think? A lot of atheism to me seems born of despair, with a pervasive bitterness, searching for further proof, particularly by convincing others, of their worst fears and suspiscions. Often clinging to singular, myopic and over simplified moral precepts in the process.
On the other hand I could be only witnessing one kind of atheism, the perspectives of the materialists or cult of reason or even Epicurious are more hopeful and hold out a desire for freedom from fear of vengeful spirits, capricous ancestors or dieties.