Defining what is and is not a religion is something I am not willing to do. How can you say Christianity is a religion, but reject Scientology as simply a cult? Both are crazy, both help people, and both have believers.
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First of all, defining atheism is like defining religion: you will get as many answers as you get people. No ONE definition is exactly right, or even accurate.
I am an atheist, and really enjoy Dan Barkers work. Here is a quote from him: It turns out that the word atheism means much less than I had thought. It is merely the lack of theism [...] Basic atheism is not a belief. It is the lack of belief. There is a difference between believing there is no god and not believing there is a god — both are atheistic, though popular usage has ignored the latter [...]
Some atheists simply talk about doubt, however as with anything, there are extremists and nut jobs.
I like this quote too, but I can't remember who its from and goes something like this: "If you accept your religion as the only religion, and do not believe in any others, then you should understand why I don't believe in yours."
My favorite thing is when Christians talk about the separation of church and state.....like it exists. "In God We Trust" on our money, swearing on a bible in court etc.