Is atheism a religion? No. Atheism is the opposite of theism. Opposites are, by definition, not the same thing. However, it seems that many people do put that definition on atheism (And some courts. Although I haven’t studied it in depth, in this case, it seemed to be a way to ensure an inmate was able to exercise free speech. I welcome any comments from folks in the know.)
I posit the root of the problem causing this confusion is how we use language. Duh, I know. Anyway, let me use evolution as an example.
On a recent episode of Hardball, Chris Matthews continually uses the word ‘believe’ in regards to the science of evolution. Science is not about belief. It is about ‘knowledge covering general truths of the operation of general laws, esp. as obtained and tested through scientific method [and] concerned with the physical world.’ Nothing in the description of science even references ‘belief’ or ‘believe.’
One of the definitions of ‘belief’ is ‘confidence in the truth or existence of something not immediately susceptible to rigorous proof.’. Seems to be the opposite of science to me.
You see this language problem with atheism. Many people use the phrase (or some variation thereof) ‘Atheism is a belief system.’ Somehow they feel that the absence of belief is the same as belief. Could it be because they are so vested in belief of something, anything, that they cannot get outside of the box and comprehend that lack of belief is just that? The non-existance of belief? I don’t know.
I have heard some atheists use the same language. I propose we get a little more disciplined and purge the word ‘believe’ when talking about atheism. I’ll use evolution again as an example because it’s just so darn easy. For instance, instead of asking ‘Do you believe in evolution?,’ ask ‘Do you accept the scientific evidence for evolution?’ At the end of the day, that’s what it’s about. Accepting or rejecting the science. With regards to atheism, when someone says ‘You atheists believe in this or that!,’ remind them, no level of belief is involved. There no deity that requires a denial. There is simply nothing there requiring any type of acknowledgement (and denial can be considered a form of acknowledgement). Do it gently, do it forcibly; whatever works best for you. But get away from declaring belief/not belief. Frame the dialogue in your words, not theirs. You may even get a decent debate out of it.
Great Site: The Council for Secular Humanism.