Religious people try to assert the idea that atheism is itself some sort of religion. Maybe this is because these people are so caught up in their own religious beliefs that they cannot imagine any person living without religion of some sort. Maybe it is due to some persistent misunderstanding of what atheism is. And maybe they just don't care that what they are saying really doesn't make any sense.
Ricky Gervaise
Atheism isn’t a belief system. I have a belief system but it’s not “based on” atheism, it’s just not based on the existence of a god. I make none of my moral, social, or artistic decisions based on any god or superstitions. Saying atheism is a belief system is like saying not going skiing is a hobby. I’ve never been skiing. It’s my biggest hobby. I literally do it all the time.
Short Answer
Atheism is not a belief system - any scientifically minded atheist confronted with a testable proof of the existence of god would surely accept it in the same way as any other scientific theory. There is simply no such proof, or even evidence, so far.
It is the theists who have the belief systems, and they are the ones who have to justify their statements about the supernatural or be seen to be fantasists. I look forward to the proof of the existence of your fairies, but shall not hold my breath.
Atheism is the absence of god-belief.
All else is embellishment. Atheism has no dogma, no rites, no holy books, no places of worship and no clergy of any description. It offers no moral guidance, no political opinions and no world view.
It is not a religion.
Long Answer
Does atheism have anything approaching "clearly defined rules?" Not in the least. There is only one "rule," and that is the rule of the definition of "atheism" - not having any belief in any gods. Other than that, atheists are free to do whatever they want and still be called atheists. An atheist can do and believe absolutely anything beyond gods and still fit the definition. Quite the opposite of how "rules" are treated in a religion.
Does atheism contain "...a philosophy by which to live?" Atheists certainly have philosophies by which they live. A popular philosophy might be Secular Humanism. Another might be objectivism. Still another could be some form of Buddhism. There is not, however, a clearly defined philosophy common to all or even most atheists. In fact, there is nothing inherent in the disbelief in god(s) which leads a person to any philosophy of life. Quite the opposite of how 'philosophy of life' is treated in a religion.
Atheism is a disbelief, not a philosophy. My disbelief in the Tooth Fairy is not a philosophy of life - is it for anyone else? Furthermore, a philosophy of life is not necessarily a religion and it doesn't necessitate that a religious belief exists in the person with the philosophy.
Religions has its leaders, the preachers of its tenets. So does atheism (Nietzsche, Feuerbach, Lenin, Marx). All of those philosophers disagreed in many ways - thus supporting my contention that atheism, as such, does not have any set of "clearly defined rules" and is not a single religion. Many atheists, in fact, have no interest in those authors.
Religionists love to equivocate upon the term "faith." Faith has multiple meanings - not all of which are exactly the same. The sort of faith to which I refer above and which one might consider common among atheists is that of simple confidence based upon past experience. Moreover, that faith is not limitless - it should only go as far as evidence warrants. In religion, however, faith means a great deal more - it is, in fact, essentially a belief without or in spite of evidence.
A religion doesn't have to have leaders, an eschatology, defenders, etc. to be a religion. Just because something does have those things doesn't mean that it is a religion.
Perhaps it would also help to examine what a religion is. The Encyclopedia of Philosophy, in its article on Religion, lists some characteristics of religions. The more markers that are present in a belief system, the more "religious like" it is. Because it allows for broader grey areas in the concept of religion, I prefer this over more simplistic definitions we can find in basic dictionaries. Read the list and see how atheism fares :
1.Belief in supernatural beings (gods).
2.A distinction between sacred and profane objects.
3.Ritual acts focused on sacred objects.
4.A moral code believed to be sanctioned by the gods.
5.Characteristically religious feelings (awe, sense of mystery, sense of guilt, adoration), which tend to be aroused in the presence of sacred objects and during the practice of ritual, and which are connected in idea with the gods.
6.Prayer and other forms of communication with gods.
7.A world view, or a general picture of the world as a whole and the place of the individual therein. This picture contains some specification of an over-all purpose or point of the world and an indication of how the individual fits into it.
8.A more or less total organization of one's life based on the world view.
9.A social group bound together by the above.
No atheism isn't a religion. If it were then the list of religions we'd all be members of would be unmanageable; ateapotism, aunicornism, afairyism, awerewolfism, agoblinism etc.
We Are All Atheists
"I have found it an amusing strategy, when asked whether I am an atheist, to point out that the questioner is also an atheist when considering Zeus, Apollo, Amon Ra, Mithras, Baal, Thor, Wotan, the Golden Calf and the Flying Spaghetti Monster. I just go one god further."