Agnostics

[Excited Penguin]

That is simply inacurate. Lack of belief is an acceptable form of atheism. Lack of knowledge of existence of belief is perfectly compatible with atheism as well.

Certainly, I lack belief in God myself rather than expressing certainty in the nonexistence of any kind of God or god (I am a gnostic atheist regarding the tri-Omni version and literal Biblical version, however). Lack of knowledge of existence of belief renders atheism not even an opinion, and I think it is at least that.

But I'm aware that my opinion doesn't represent the majority here. I don't think it's splitting hairs to observe that a rock isn't a person ant that the suffix 'ist' can't apply to a rock, though. A rock does fit the definition of 'atheist' that you give though: it does lack knowledge of existence of belief.

Atheism is not an opinion. Far greater minds than yours or mine agree with me on that, if "mere" logic doesn't convince you. Atheism is the description of a non-state, it is the default position - it is natural. Where there is lack of theistic belief within an intelligence, you have atheism. There's nothing wrong with that, it's just something to describe all the people in the world who don't believe in Gods. Do we need the word? Yes, it's unfortunate but we need it. Why?  Simply because theists are the majority.