I don't think you're right about that Red Dog. TGD, as one example, is concerned with the lack of supporting evidence for the God hypothesis. I know only a handful of non-believers who put themselves in the gnostic category.

You are right that "pedophile" is more than the sum of its parts, but "atheism" is not. "Theism" is a description of a belief-state; "atheism" is its antipathy.

Comment 4 by Red Dog :

I disagree. You can't define the meaning of a word simply by analyzing its component parts. The usage is all important and the meaning of words is changing constantly. Consider the word pedophile. If you break it down into its component parts it just means someone who loves children. Obviously the actual meaning is radically different.

The way atheism is used in the works of Dawkins, Harris, etc. and what most people on this site and elsewhere mean by it is not just a neutral lack of belief in any God but an affirmative belief that there is no God.