Atheism MIGHT be a belief, but only if a person holds the philosophical/quasi-religious position, "I believe God does not exist."
That person has stated a belief. (As for it being a "system," well, that's a whole other matter).
On the other hand, when a different person clearly expresses this thought, "I do not believe in God," that is a far different thing. Here they are articulating a lack of belief.
They could have different reasons for this, but most often (from what I've observed) they simply do not find the arguments for belief in God to be convincing.
The point I am making is not merely a matter of semantics, but rather it is a very important philosophical point: Having a belief--no matter what it is--is not the same as NOT having a belief. They just aren't.
I find that one of the biggest problems in these kinds of debates is that the average person does not think clearly; in fact, they are mostly very sloppy in their thoughts. The matter gets compounded when they speak these convoluted, unclear thoughts out loud (or type them on a keyboard).
Then, when they are misunderstood, they get their knickers in a knot. Pretty funny considering the confusion started inside their own head.
Learning to think clearly and to express yourself clearly is a very difficult thing. It takes a lot of hard work, a lot of mistakes, a sense of humility and the ability to not take yourself too seriously when others offer constructive feedback.
Anyways, those are my beliefs, ... for what it's worth!
