The reason such an explanation does not apply to usage of the term "atheism" is that we can trace the history of the attempt to dilute the term for rhetorical purposes.<quoted text>
You can use a word in any way you want as long as you define your usage and use it consistently.
And if enough other people find your choice useful and agreeable, they'll start using it the same way.
Following that, it might appear in a dictionary, which will surely frustrate and infuriate rigid, controlling types.
An effort to change the meaning of a term, which applies to millions, and whose meaning is clearly understood, so as to service an agenda of one side in a controversy, is far from the innocent evolution of language you pretend.
Don't try to kid me.