You said: "You can't have a belief in atheism. That would be a belief in lacking a belief in god(s)." I took that to mean atheism does not involve beliefs. Plainly it can do … ie strong atheism.
I just happen to come across a 1976 Webster's dictionary yesterday … it only gave the strong atheist definition. Apparently the word atheism came into the English language around the 1500s from wiki: The term atheist (from Fr. athée), in the sense of "one who ... denies the existence of God or gods",[134] predates atheism in English, being first found as early as 1566.
and
The term theism derives from the Greek theos or theoi meaning "god". The term theism was first used by Ralph Cudworth (1617–1688).[8] In Cudworth's definition, they are "strictly and properly called Theists, who affirm, that a perfectly conscious understanding being, or mind, existing of itself from eternity, was the cause of all other thing
So it would appear the term atheism(t) may predate theist in the English language. But note the early use of the strong definition of atheism.
Here is an essay from SEP that is pushing (back) for a strong definition of atheism.
Being both atheist and agnostic I agree is a perfectly logical position to hold. And broadly that would be mine assuming we are using the weak definition of atheism.
My apologies for the word stasi. It was meant to be amusing