Thanks for the clarification on linguistic history.
In the same way certain bible thumpers relish the thought of parading their "salvation" to the children of the damned (aka, the rest of us), I believe there is a small subset of anti Christian zealots who fully realize the word "atheist" has maximum annoying effect on bible thumpers.
Some of it depends on what is meant by the word "God" or Gods. An anthropomorphized literal interpretation of a Judeo-Christian God straight out of the Book of Job is obviously an easy target of ridicule. Even Catholic, Orthodox, and mainline Protestants believe God is utterly incomprehensible and cannot be literally imagined in the human mind. More broadly, in world religious tradition, Gods, deities, spirits are just different faces humans put on a spiritual truth or higher reality underlying the universe.
I agree that agnosticism is the posture which most likely is reached through the exercise of reason. Unequivocal, definitive certainty that there either is, or is not a spiritual dimension, a higher reality to the universe is not the sort of posture which can be arrived at by reason. Reason and human cognition are going to fail us sometimes. We are not omniscient beings - we basically only have the brains of a souped-up chimpanzee.