Consider for a moment how very easy it was for me to get a whole bunch of Atheists really, really upset in this thread. Why? Because I had the temerity to tell them what Atheism is, when they had their own interpretations of what Atheism is that did not match what I was saying.
If you're not an atheist, Trevor, then going around to actual atheists and telling them what they really believe is sure to get up their noses.
Here's the first thing that google turns up when I enter "atheism as a belief" (with my emphasis added):
Atheism is usually defined incorrectly as a belief system. Atheism is not a disbelief in gods or a denial of gods; it is a lack of belief in gods. Older dictionaries define atheism as "a belief that there is no God."
I am an atheist and I agree with that definition. I do not have a belief that there is no God, much less a belief system. Arguing that an atheist believes in no-God is as irrelevant as a goldfish espousing a belief in the water he's living in. It is a supremely unrewarding line of thinking and thus we can, and do, safely discard it.
PS, as someone else mentioned, there's a difference between a-theist and anti-theist. The hint is there in the prefix; a- means "without"; whereas anti- means "against". I am without the baggage of belief in a god (ie, I call myself an athiest), and also without the baggage of having to believe that there is none (I am not an anti-theist).