1. Positive View/Position:
The definition of atheism as a "belief" or "doctrine" reflects a view of atheism as a specific ideological stance, as opposed to the rejection or simple absence of a belief.
In philosophical and atheist circles, however, this definition is often disputed and even rejected. The broader, negative has become increasingly popular in recent decades, with many specialized textbooks dealing with atheism favoring it. One prominent atheist writer who disagrees with the broader definition of atheism, however, is Ernest Nagel, who considers atheism to be the rejection of theism (which George H. Smith labeled as explicit atheism, or anti-theism): "Atheism is not to be identified with sheer unbelief... Thus, a child who has received no religious instruction and has never heard about God, is not an atheist—for he is not denying any theistic claims."
Some atheists argue for a positive definition of atheism on the grounds that defining atheism negatively, as "the negation of theistic belief", makes it "parasitic on religion" and not an ideology in its own right. While most atheists welcome having atheism cast as non-ideological, in order to avoid potentially framing their view as one requiring "faith", writers such as Julian Baggini prefers to analyze atheism as part of a general philosophical movement towards naturalism in order to emphasize the explanatory power of a non-supernatural worldview. Baggini rejects the negative definition based on his view that it implies that atheism is dependent on theism for its existence: "atheism no more needs religion than atheists do". Harbour, Thrower, and Nielsen, similarly, have used philosophical naturalism to make a positive argument for atheism. Michael Martin notes that the view that "naturalism is compatible with nonatheism is true only if 'god' is understood in a most peculiar and misleading way", but he also points out that "atheism does not entail naturalism".
2. Negative View/Position:
Among modern atheists, the view that atheism simply means "without theistic beliefs" has a great deal of currency. This very broad definition is often justified by reference to the etymology (cf. privative a), as well as to the consistent usage of the word by atheists. However, others have dismissed the former justification as an etymological fallacy and the latter on the grounds that majority usage outweighs minority usage.
Although this definition of atheism is frequently disputed, it is not a recent invention; as far back as the eighteenth century, d'Holbach (1772) said that "All children are born Atheists; they have no idea of God". More recently, George H. Smith (1979) put a similar view:
"The man who is unacquainted with theism is an atheist because he does not believe in a god. This category would also include the child without the conceptual capacity to grasp the issues involved, but who is still unaware of those issues. The fact that this child does not believe in god qualifies him as an atheist."
Smith coined the terms implicit atheism and explicit atheism to avoid confusing these two varieties of atheism. Implicit atheism is defined by Smith as "the absence of theistic belief without a conscious rejection of it", while explicit atheism—the form commonly held to be the only true form of atheism—is an absence of theistic belief due to conscious rejection.
Many similar dichotomies have since sprung up to subcategorize the broader definition of atheism. Strong, or positive, atheism is the belief that gods do not exist. It is a form of explicit atheism. A strong atheist consciously rejects theism, and may even argue that certain deities logically cannot exist. Weak, or negative, atheism is either the absence of the belief that gods exist (in which case anyone who is not a theist is a weak atheist), or of both the belief that gods exist and the belief that they do not exist (in which case anyone who is neither a theist nor a strong atheist is a weak atheist. While the terms weak and strong are relatively recent, the concepts they represent have existed for some time. The terms negative atheism and positive atheism have been used in the philosophical literature and (in a slightly different sense) in Catholic apologetics.
Contrary to the common view of theological agnosticism—the denial of knowledge or certainty of the existence of deities—as a "midway point" between theism and atheism, under this understanding of atheism, many agnostics may qualify as weak atheists (cf. agnostic atheism). However, others may be agnostic theists. Many agnostics and/or weak atheists are critical of strong atheism, seeing it as a position that is no more justified than theism, or as one that requires equal "faith".
3. Atheism And Intelligence:
According to a study by Paul Bell, published in the Mensa Magazine in 2002, there seems to be an inverse correlation between intelligence and religious belief. Analyzing 43 studies carried out since 1927, Bell finds that all but four reported such a connection, concluding that "the higher one's intelligence or education level, the less one is likely to be religious or hold 'beliefs' of any kind." A survey published in Nature confirms that belief in a personal god or afterlife is at an all time low among the members of the National Academy of Science, only 7.0% of which believed in a personal god as compared to more than 85% of the US general population.
That's not to imply that anyone is stupid for believing religion. Just that skepticism/cynicism is something that appears to grow especially so the more you know.