". . atheism is a word, words have definitions and the primary and original definition is "the belief that God doesn't exist". You don't need to "pull anything out" because there's no contradiction."
In ordinary usage I fully accept that theist = believer in God, and atheist = disbelieves god's existence. We all know that words and their meanings evolve and drift over time and currently many dictionaries will define these words in the way commonly understood. Fine.
But think about this, what if a dictionary defined 'Christian' as "a member of any of certain Protestant churches, as the Disciples of Christ and the Plymouth Brethren." (see here) I bet most of you Christians would reject that definition point blank.
Well I reject the definition of 'atheist' as someone who definitely 'believes' that there is no god and, more to the point, so do almost all atheists!
Take the moon landings as an example. Many Americans believe that the moon landings were faked - let's call them moonists (I was tempted to say lunatics). Moonists are currently in the minority, though a sizable one it must be said. If the issue of the moon landings ever moved from the trivial to the serious you might be forced to declare your view on the matter whereas at present you do not define yourself by this irrelevant (to you) issue. However, if pressed you would have to declare yourself to be a moonist or not. Would you actually use the word amoonist if you believed that the moon landings in all likelihood did happen just as the history books record? I doubt it.
So why should men & women who are not theists be forced to attach labels like atheist to themselves? Only because the idiocy of god-belief has become so widespread that rational human beings are forced to say "sorry, I don't share your belief, I'm an atheist".
Again, atheism is not the belief that there is no god, it is the lack of belief that god does exist.