Why? I think of how alone I felt for 30+ years not having a group that I could discuss, disagree, debate, etc without having to watch my back for knives. Why? I've forged my attitudes and thoughts over the years without the benefit of mentors. Yes there was the occasional book, but nothing that could help with issues that could pop up from time-to-time. I know I'm 50+ but that doesn't mean that I cannot learn from someone younger. Why? There are so many people here that have a different background than I do. There are ex- Christians, Muslims,, etc...and even practicing members of their religion. There are young, old, American (North, Central, and South), European, Mid-Eastern...I love it! Why? I can ask a question that consists of a powerful three letter word...why.
Since I don't believe in any gods, thinking atheist is my default mode of thinking. I can easily think theist, but it requires conscious effort.
If you meant why I'm here: it's nice here. Nice people, civil discussions, and most of all - almost everyone is ready to call bullshit on anyone else, no matter who they are. But are mostly polite about it.
Because no one in my life knows anything about religion, but many of them would disown me if I spoke my mind openly on the subject. I have learned here. I have taught here. I think that the cycle will continue. It's a sanctuary.
Well, because its one place where I can write 'Atheist' in 'Religious Section'. Because this is one place where I can find most number of decent, civilized humans who are willing to debate, educate and exchange ideas. And because its one place where I do not get spammed (almost) with any religious messages :-)
This reminds me of a small conversation I had with my father. He came into my room and asked what I was doing. I was playing a game, so I said so. It happened to be a strategic WWI game. He said something stupid - I forget what, so I jokingly replied "You can deny evolution (though not really) but you cannot deny WWI." He said something about Jehovah's Witnesses believing the hogwash that 1914 marked the beginning of the last days before armageddon. I told him I didn't want to talk about religion (hearing about it at the wrong times pisses me off) and he insisted I started it. I replied "No, I was speaking about evolution, not religion. Keep talking about religion if you want then, let's see how far that goes." I tire him out when we speak about religion, I must make him think too much (or at all). He then replies "I can't 'masturbate' my mind as much as you do." To which I said, "You mean use it?" He absentmindedly said "yes" and I got a good laugh out of it. He had a bit to drink so there was a chance that he wasn't really paying attention, but it sums up perfectly how I feel with my position and his. I think, therefore I'm a skeptical atheist. He doesn't and therefore he's an inconsistent theist.
The question could be, why do you think? - as soon as you do you have to end up atheist/agnostic. The liberation in atheism to me is that every second is precious, it makes living more tangible and that as 'god does not have a plan for me'! I can shape my own world, so I am the creative force in my life. Atheism brings humanity closer and adds a sense of responsibility. We can no longer rely of the duality of body and spirit, and must stand accountable for our actions - the devil did not make me do it, and god can't forgive me!
Its a better, more real and energising place to be.
Try Kipling’s Six Honest Serving men (they taught me all I knew), their names are what and why and when and how and where and who......The real beauty is every unfolding evolutionary moment is an ABSOLUTELY new uncharted experience.
As others have said, it is where critical thought leads. Faith, as a concept, was not enough for us. Faith is religions duct tape. When it starts to fall apart just tape it up...and shut up. There were so many fallacy's in religions premise and implementation. Not to mention it's outlandish claims. The idea that god could simply adjust the laws of physics to accommodate menial acts or people, without the consequence of the law being broken, was too much. It's easy to suspend disbelief in fiction, but when you are expected to believe that people come back from the dead or fly or the molecular properties of water were once changed to wine, is too much to ask without proof. And that's where faith comes in. But I see faith as a fancy way of saying "Shut the fuck up!"
Atheism is not an alternative to religion. Just like Janis said, it is a default to not believing. If all the world stopped believing in god there would be no more Atheists. So, why think Atheist? Ask a bald man why he is bald. Because he has no hair.
Maybe you are asking why we are here on this site? Well, I think everyone has covered that. Humans require a tribe to share ideas and find comradery. We seek solace in a predominately religious world. A place where we don't feel like we're bashing our heads against a wall. Trying to convince a dog that "quantum mechanically entangled particles must violate either the principle of locality or the form of philosophical realism known as counterfactual definiteness." But that's relative to our plight.