An atheist is a person without a belief in any god. It doesn't matter why you don't believe in God. If you have carefully and rationally examined the evidence, found none for a god, and therefore you don't believe, you are not "more atheist" than some kid who is angry because his first girlfriend dumped him and decided God doesn't exist. There is one and only one criteria for being an atheist: you don't believe.
This is why I don't believe in agnostics.
Oh, I believe that there are agnostic people out there; the problem is, they are also either believers or atheists. It is simply impossible to be between belief and non-belief. Most agnostics are atheists who are afraid to admit it.
All of those people who say, "I don't know" or "I don't care" or "I don't think we can know" don't believe in God. They are atheists. That they don't believe because they haven't made up their mind, or don't think there is a way to prove it, is irrelevant, because the only criteria for being an atheist is that you don't believe. These people calling themselves agnostic does a fine job of telling us why they don't believe in God, but it doesn't make them somehow in a middle ground where they neither believe nor disbelieve. If they say they neither believe nor disbelieve, they still don't believe. That's covered in the neither part — that they followed it up with "nor disbelief" doesn't change that. Not actively disbelieving in God doesn't mean they don't still passively lack belief in him.
And I would be willing to bet that the vast majority of people who do believe are agnostic, too. I've heard a million times Christians saying something to the effect of "well, I really don't know, but believing makes me feel better" or "there's really no telling, but for me, believing feels right." These people are all agnostics, too. Most people are agnostics, when you get down to it, making the term so all-encompassing as to not have a whole lot of value unless you're specifically having a conversation about the topic of how and why people believe.
Agnosticism doesn't have anything to do with belief. It has to do with the limits of knowledge. There are agnostic atheists and agnostic believers all over the place, but there are no just-plain-agnostics.