Is atheism a religion? Is bald a hair color?

So, many times I come across theists (specifically Christians) who refer to atheism as a 'religion'. I don't know why they do this, personally; perhaps it's a drastic attempt to reassure themselves that a human cannot possibly lead a fulfilling, moral life without a religion to follow, but regardless of the reason, the topic comes up regularly.

The short, sarcastic answer to this question is, "Atheism is a religion like not collecting stamps is a hobby." I've also seen, "Atheism is a religion like bald is a hair color."

Barbed wit aside, let's actually take a look at a detailed definition of 'religion' (from Wikipedia):

"A religion is a set of beliefs concerning the cause, nature, and purpose of the universe, especially when considered as the creation of a supernatural agency or agencies, usually involving devotional and ritual observances, and often containing a moral code governing the conduct of human affairs."

All right, that seems pretty clear to me. I can sit down and show how Christianity, Islam, Hinduism, and so forth fulfill that definition.

Now let's look at atheism, and see how it stacks up.

"...a set of beliefs concering the cause, nature, and purpose of the universe..."

Atheism is a single belief (or, arguably, a lack of belief) in a single concept - that of the existence of gods. If a religion is a "set of beliefs" (and I've yet to come across a single religion that had only one tenet), then atheism is disqualified, as it only specifies one philosophy. Additionally, that concept does not speak toward the cause, nature, or purpose of the universe, so that's strike two.

"...especially when considered as the creation of a supernatural agency or agencies..."

Supernatural agency = gods. Since atheism is a lack of belief in the existence of such beings, that's strike three. If this were baseball, the "atheism is a religion" team would already have struck out, but let's continue.

"...usually involving devotional and ritual observances..."

While blogging, answering questions on Yahoo! answers, and hanging out at Starbucks might be common amongst atheists, I would not term them either devotional or ritualistic - nor are they universal.

"...and often containing a moral code governing the conduct of human affairs..."

When atheism itself is a simple statement of lack of belief, how could it be considered to offer any sort of moral code? Atheists propose no unified moral code. It offers no guidance in itself. It's really a simple statement - along the lines of saying, "Without evidence of gods, why believe in them?"

So is atheism a religion? Sure doesn't look like it to me. In this ballgame, that concept has struck out.