Had this argument in a bar last night. The problem is that when many people become athiests, it becomes their new religion. They forget that there is a religious impulse that also drives them to seek conversions to their cause. For many (I cant say all) people I have met, their religion becomes "Christians are stupid".
Also tie in the ego-kick that many people get when they find somebody that they can claim to be stupider than themselves. Hence all the "Chimphitler" remarks and such. Its a quick way out for real losers.
That aside, I am reading Dawkin's "The God Delusion" right now and its fairly well written. Unfortunately, he himself is what we can call a "religious athiest".
This loosely ties in with what C.S. Lewis was writing about decades ago. His thesis was that all people are "hard-wired" to believe in more than the existential world, in something larger than one's self.
But when God is removed from the equation, this can take many, perhaps bizarre, forms.
In true atheism, one's self becomes one's God (this also works for Communism,) which explains why such believers take perceived insults so personally, even when no insult is present or implied.
If environmentalism is the adopted religion, then God is "Gaia," even if not accompanied by ceremony.
In Nazi Germany, the State was God.
With little expansion, this expands to Druidism, Wicca, animal-rights activism, a host of other things.
The common thread is "fervor." The "annointed" have the same zeal as any traditionally religious person, but it guides their actions into sometimes unrecognizable realms.
But without the moral compass of a God-based faith, things quickly spin out of control. Just look at the headlines on any given day.
All atheists see their God when they look in the mirror.