The essential nature of atheism is denial, which is different to the kind of materialism, and the the scientific positivism put forward by StrawberryFrog, and also the (admittedly) solipsistic approach of xunker. While both of these are noble interpretations of the rationalisations that surround atheism, they don't deal with the central denial that is the necessary and sufficient condition for identification of an atheist.

Is atheism a crutch for the weak? Or put another way, why would one *deny* the existence of God? There is so much richness in that one word, deny, an entire spectrum of emotion, and whole vistas of personal psychological reasons that I think it's really beyond the scope of this writeup to cover them all. However I will point out that the denial takes place despite the much more moderate approach of agnosticism, which is much more in line with the kind of scientific revisionist principles extant today, which would allow one to keep an open mind on the existence of God. An atheist by contrast doesn't just deny the existence of God, but also in most cases would deny belief in Him, even if shown proof he existed.

Why is this? Surely it must make some critical difference to the person involved, otherwise they wouldn't take this stance. Personal experience has taught me that many of the atheists I know take up their positions either to escape from social nets in which a belief in God may trap you, or because they feel that at some point in the past their belief in God was shattered by a tragedy. There are rare cases of individuals growing up without any belief in God whatsoever, but one finds that they are usually tied to some sort of religious system that precludes a vizualisation of an overall force (some parts of Hinduism do this). In the first two instances, one could definitively say that the person is moving away from sources of strife, or in the latter case, personal pain. These are real motives, but have very little if anything to do with the scientific or logical validity of a belief in God. One finds that often, as the social networks become more open and tolerant, (ie their participants mature and learn not to evangelise), or that the pain of the personal tragedy is dissipated through therapy or personal growth that atheists tend to mellow.

The crucial point here is that the logic that would ordinarily convince a person of the validity of a/theism will not have any ground to stand upon unless the underlying emotional framework is stable and secure, and when it is, there is no longer any need to run away, and the person becomes open to all possibilities including the existence of God. In effect, they no longer feel the need to deny. That doesn't mean they feel the need to accept either, but again that's a personal choice. I would view atheists much as I would view evangelists, both sharing a need to define themselves by their denial of areas of common human experience and thus limiting and sharpening their own identities in their minds eye.

I guess when that image becomes untenable, then like people of all persuasions, religious or otherwise, they change.