Not believing something is not necessarily an article of faith. Not believing something because it conflicts with one's religious beliefs may well be an article of faith, but a good deal of the refusal to believe something arises from skepticism--arises from rejecting an idea for the lack of evidcnce.
Let's start with the definition of faith from Merriam-Webster's online dictionary (a preferred source for Americans):
Quote:1
a : allegiance to duty or a person : loyalty
b (1) : fidelity to one's promises (2) : sincerity of intentions
2
a (1) : belief and trust in and loyalty to God (2) : belief in the traditional doctrines of a religion
b (1) : firm belief in something for which there is no proof (2) : complete trust
3
: something that is believed especially with strong conviction; especially : a system of religious beliefs <the Protestant faith>
For the purpose of your question (if i have read you correctly), we can discard definition one, as that does not seem to be what you are asking about. I think, rather, that you are referring to definitions two and three.
I was rather surprised by definition 2 b 1. I would not have thought that an authoritative source would have taken a stance on the subject of whether or not there is any proof for a deity. Personally, i don't know of any evidecne for a deity, so i don't believe that there is one. I was just surprised to see Merriam-Webster taking a position on the matter.
Somone might take a position on something based on their faith in an authority. So, in the 18th century, many people were confidently predicting that no new bodies would be found in the solar system. Many people had faith in that pronoucement because the people speaking were considered authoritative. However, in 1801, the asteroid Ceres was discovered (it is now considered to be a dwarf planet--it's about 600 miles in diameter); people who accepted the notion that no new bodies would be found in the solar system because they took it on faith by authoritative statements were disappointed.
Religious belief is much the same circumstance. It is more compelling, however, because children are told about "god" and the popular religious confession of their community by their parents, otehr family members, other children, teachers and respected adults in their community. In addition, the ministers of their religious confession will assure them that there is a god, and that the tenets of their religion are supported by scripture--treated as an authoritative source--as well as the teachings of people who are alleged to be authoritative. Many people who believe in god and the particular tenets of their religious confession have believed it all their lives, and will not just ignore claims made against their belief, they will resent any such claims.
Generally speaking, the lack of a belief is very likely not a matter of faith. I have pointed out an excellent example of people not believing something on faith (i.e., not believing that any new objects would be found in the solar system because allegely authoritative people had decreed that it was do). However, that is a rather uncommon and tortured example.
There are two broad categories of atheists, if one ignores that there are about as many forms of atheism as there are atheists. There are the strong, or explicit atheist, who says "there is no god." That can well be seen as a kind of backhand faith, in that such an individual is not providing any proof. It is, however, based on the logical fallacy
argumentum ad ignoratiem, the appeal to ignorance. It basically says that if we don't know that something is true, it must not be true--we don't know to a certainty that there is a god, so there must not be a god. I don't care that there are such atheists, and their argument is pretty well founded, because the burden of proof of any claim is clearly on the person making the claim (that is, in this case, the person claiming that there is a god). But to my mind, that leads to what is called weak atheism, or impolicit atheism. I know of no reason to state categorically that there is a god, so i don't believe it (and i also don't care). But, i also know of no reason to state categorically that there is no god. Once again, i don't really care. I simply don't believe. There is no article of faith involved.