I can feel your anger

[Skepsis]

Now, it seems to me that Atheism is also a big umbrella; it includes secular humanism, nihilism, naturalism, etc. The common property is that every belief system in Atheism fails to include the belief, "At least one god exists".

Which makes sense from a macro point of view, too; under this view, Atheism is the complement of Theism. It includes everything that isn't in theism--i.e., every belief system that lacks theistic belief.

Really and seriously? I can't believe you are seriously arguing the most cliched anti-atheist argument on the books- that atheism is a belief system. Most people go from that to "So you must have as much faith as us" (as if that should be an insult coming from the faithful), or they say, "So, anyways, not that that's established, take my burden of proof".

But you...

You're an odd one. You simply argue to argue, don't you? I think it's silly to argue that atheism is a class as theism is. Atheism, as you freely confess, is the lack of belief. You say that, then you contradict yourself, saying that atheism includes all beliefs that don't fall under the theistic umbrella- which is obviously wrong. Atheism is a lack of belief, or hell, you might even call it the rejection of theistic propositions- but it certainly isn't a belief, and I would happily shoot myself in the foot if you can show me that it's a "belief system".

What utter garbage. Do you even think before you post?
No- Sorry. I don't mean to get too snippy.

But I still think your argument is absolute trash.

Man, it's like the atheists here are allergic to things like mathematical abstraction, logical formalism, methods of inference, and intellectual curiosity.

We're allergic to arguments that have been covered in detail thousands of times before, on the internet, in real life, and on these very forums. This argument might very well be the oldest and stalest in the "theists' shitty arguments" list.