My friend asked me a question the other day. He said he has observed atheists becoming more and more like a religion so when does it get considered a religion? This was my best reply with the aid of a dictionary.
The simple answer is that atheism WILL NEVER be a religion. Why?
Because atheism is NOT a set of beliefs about cause, nature, and purpose of the universe. Atheism is the observation there is no evidence for gods. That's it. Atheists can also accept evolutionary theory - or not - but atheism does not advocate a set of beliefs in the ways religions do.
Next, since atheists observe there is no evidence for gods (and/or the supernatural) it also cannot be a religion.
Third, there are no atheist rituals or observances. Therefore it cannot be a religion.
Fourth, atheism does not have views about how people should live morally. Instead of looking to supernatural agents for moral instructions atheists use their reason and compassion - however this too is SEPARATE from the observation there is no evidence of any gods.
So once we actually understand the necessary and sufficient conditions for what qualifies as a 'religion' it's pretty easy to see that calling atheism a 'religion' is either wrong or bone-headed (depending upon whether the person understand atheism cannot be a religion but refers to it as one anyway).