One thing that has particularly aggravated me about atheism and theism is the lack of specificity when one begins to discuss the existence or nonexistence of a god. When one says, "I'm an atheists" or "I'm a theist" I usually am like "okay, so is my pet orangutan...and....?" Of course I'm not serious about this, but it is a way to let one know that what they are saying needs to be clarified. While it is certainly true that a theist who claims that a particular deity exists bears the burden of proof for that particular deities existence, at the same time I do not think it is right for atheists to make categorical statements about being atheism without reason, because atheism seems to be more of a category of positions than any single position about god.
When categorically dealing with atheism then, atheists are typically divided into two groups: "strong" and "weak" atheism, which often correlates to "positive" and "negative" atheism respectively. Positive atheism is the assertion that, "I believe that no gods exist", while "weak" and "negative" atheism is the assertion, "the existence of gods cannot be known, therefore I do not believe in gods." These two categories are often called "explicit" atheism, while a third often touted category of atheism is "implicit" atheism. The atheists in this category are those who have no beliefs about god. (I call this ignosticism.) The categories above define categories of atheism based on the strength of assertions, but when we begin to discuss atheism, there are really two areas that we talk about: "belief" and "god". These two areas fall into two categories, namely epistemology and ontology respectively.
Epistemic assertions are assertions about the nature of beliefs and knowledge. The post "Am I an Atheist or Agnostic" seems to handle the epistemic side of atheism by asserting that agnosticism and ignosticism definitionally, are forms of atheism because those who hold such beliefs do not have beliefs in a deity. When we begin to discuss this however, the epistemic reasons, such as lack of evidence, lack of cogent evidence, the meaninglessness of god talk, among others need to be noted. Aside from this, I think it is also necessary to define what can be an atheist. The post "Am I an Atheist or Agnostic" asserts that everyone is born atheists. Insofar as this is concerned rocks and trees could also be atheists, but this of course absurd. The ability to believe, then, is perhaps a prerequisite for atheism.
The ontological category of atheism is when one talks the actual existence of a god. Because "god" is a broadly applied term, one needs to specify exactly what one is asserting when one talks about "god". Normally, when one begins to talk about god, classical theism is typically the topic of conversation, but not necessarily barring other forms of god. The problem with saying does not believe in a god or gods, is that that gods can be very real things. The ancient Egyptians, for example, believed that men were gods. Numerous other religions believe or have believed that things like plants, mountains, stars, moons, planets, and animals are gods. If one were to assert that one does not believe in gods categorically, then one would not believe in these things. Not so far from home are other ideas about what one calls "god". Albert Einstein said of "god" that "I believe in Spinoza's God who reveals himself in the orderly harmony of what exists, not in a God who concerns himself with the fates and actions of human beings" and "I do not believe in a personal God and I have never denied this but have expressed it clearly. If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it." Einstein's definition of "god" was more-or-less demystified pantheistic "god". This sort of "god" is not some mere tangible item, but nevertheless is described as a god of sort. These sorts of gods do not fit into classical theism, so one stands to reason that if some physical thing is a god, then those who believe physical things are real believe gods are real. For example:
1.) Some rocks are gods
2.) Person X believes in rocks
3.) Therefore Person X believes in some gods
But this of course is invalid as it is pure equivocation, which brings be to my point: there is nothing to prevent this line of reasoning from being invalid unless one defines what one is talking about concerning gods.
Also concerning the ontological category of atheism, one needs to be clear concerning the modality of atheism. It is one thing to say that "gods do not exist" and another to say "it is not possible for gods to exist", and yet another to say "gods have never existed" or some other tense form of a statement about the existence of gods. One could still be an atheist and believe in the possibility of gods without actually believing that gods exist. When one begins to talk about such things, one needs to be certainly clear when one begins to discuss the existence of god. Richard Dawkins concedes the possibility that gods could exist, but he himself does not believe that they exist. However the actual probability of something's existence is an epistemic discussion.
All this is to say that in order to have meaningful discussions about atheism, one need to be crystal clear as to what we are talking about. Often one of the touted problems of theism is meaninglessness of particular concepts of the divine. I suppose this is true of atheism if one merely asserts that one is an atheist and leaves it at that.
“Hokey religions and ancient weapons are no match for a good blaster at your side, kid.”