"Atheism: the lack of a belief in the existence of god or gods"
This is where the true issue with the definition of atheism lies... At it's core, it has nothing to do with a belief of the 'existence' of a God. Atheism is without the belief in a God(s)... the literal definition basically means you don't hold a belief in any god. So as an atheist I can say that I haven't chosen a god, I have no belief in any particular god, but I can also say that I haven't ruled it out.
The only science behind atheism is that there is a lack of evidence for any god or gods, so no stance will be taken either way. The hardcore atheists are as dumb as the hardcore theists because neither of them know anything for certain.
I think anyone that doesn't worship a god can be called an atheist. Just because you don't hold the belief in one or many particular gods doesn't mean you are asserting the denial of any god. Show me proof. Demonstrable evidence. Show me anything that isn't personal experience and I may form an opinion based on that, but there is nothing to go on here.
Atheism and Agnosticism go hand in hand for most people. I could call myself an agnostic atheist, because I don't have a god that I worship or believe in, but I, like everyone else on this planet, don't know for sure either way. Why not just call it atheism? An agnostic doesn't hold the belief in a god either so you could call any agnostic an atheist as well. It's stupid really.