[eivarv]

Nitpick: Atheism is not a belief system.

The term denotes the lack of belief in deities, and exactly this and nothing else. This also means that it is not based on "faith" at all, as it does not posit any assumptions.

Humanism, on the other hand, can be described as a belief system.

Not to start the ball rolling in a religious debate or anything.

[mieses]

The goal of not positing assumptions is impossible and completely discarded by New Atheists and most taxi drivers.

[eivarv]

I'm not saying that atheists don't personally make assumptions, but that atheism does not.

I'm saying that the claim that atheism is a "belief system" that makes the same kinds of assumptions as religions is intellectually dishonest at best.

This is my point:

There is a difference between a belief that something does not exist (what you're talking about, and a false equivalence), and a lack of belief in that same something (what the term actually means).

Also, not all assumptions are equal: neither "New" Atheists nor taxi drivers go around believing every assumption they hear that has not been disproven.

[drugsAreBad0001]

Yours is a common misconception, but atheism is absolutely a belief system.

"I don't believe in god" is not the same as "I believe god doesn't exist".

The latter statement is of atheists. As an agnostic, I think agnosticism is the only actual "lack" of a belief system, since I don't hold a belief either way (for/against god's existence).

[eivarv]

Yours is, in fact, the misconception; I suggest you check your references. The ones I found [1-3] state that the term may be used to describe both stances. When using the it in this kind of broad sense, I think it makes sense to try to be inclusive (as we are generalizing, after all).

I've touched upon this in a reply, but atheism asserts the former - not the latter.

Additionally, atheism itself does not posit any assumptions, so I don't understand what this alleged system of beliefs would consist of. I'd really like to hear a sound argument for the assertion that it is, though.

Atheism is not an alternative to religion, so much as a rejection of religious claims – absence of belief. It might, for instance, be formulated in one personal case as something like "These claims are dubious and unsubstantiated, so I see no reason to believe in them."

This would be an atheist concluding that they do not believe in (a) god, by way of atheism (the lack of belief).

A tired analogy would be that of a lack of belief in unicorns or pixies; neither of which would constitute a "belief system".

Agnosticism states [4-6] that it is unknown (and perhaps unknowable) whether or not the supernatural exists – so one could argue that agnosticism is not really a lack of a belief system, but a lack of taking a stance or excluding any supposition.

In my own case, I'm an agnostic atheist – in the sense that I don't think that many religious claims can be tested (by their nature). I also don't think that this is a sign of a good argument, or that they should therefore be taken at face value.

[1]: http://www.oxforddictionaries.com/definition/english/atheism

[2]: http://www.merriam-webster.com/dictionary/atheism

[3]: https://en.wiktionary.org/wiki/atheism

[4]: http://www.oxforddictionaries.com/definition/english/agnosti...

[5]: http://www.merriam-webster.com/dictionary/agnosticism

[6]: https://en.wiktionary.org/wiki/agnosticism