The term "atheist" doesn't make sense to me. What should we call someone who doesn't believe the Earth is flat? What should we call someone who doesn't believe in aliens or bigfoot? "Atheist" suggests that theist is the default but this is an irrational belief so obviously it couldn't be the default.
Unfortunately, theism is still a mainstream position in the world at large. And what is more, in many individual pockets -- that is, within some individual neighborhoods, or some individual cities, or some individual states, or some individual countries -- theism is still, to this day, not just mainstream but overwhelmingly mainstream. Given this unfortunate state of affairs, it often becomes necessary to take a position in relation to this mainstream idea. And since it -- often, but of course not always -- becomes, in practice, necessary to take a position in relation to theism, therefore it become necessary (or at least, it is convenient) to have individual word(s) that denote our position(s) in respect of theism.
If by some wild chance we found, twenty years down the line following some fantastic apocalyptic melt-down of civilization, that overwhelmingly large numbers of people have started believing that the Earth is flat (or that aliens walk among us, or that invisible bigfoots -- bigfeet? -- prowl around unobserved, punishing the immoral and rewarding the virtuous), then yes, then I suggest our language may well come up, organically, with words that reflect the position of someone who does not believe in a flat Earth, or someone who does not believe in invisible aliens or invisible bigfoots (bigfeet?) in our midst.
We don’t necessarily
have to use that word, Atheism, if it makes us uncomfortable (or if we don’t move in circles where that word serves any real function). In that case, any ideas about God (or about bigfoot, or about invisible aliens) can be shot down simply by saying they’re “unscientific”, or “lacking in evidence”, instead of dealing separately with the God-issue.
But because in
some cases a theism-centered word is not necessary, that does not mean that a theism-centered word is
never necessary. Because some people find the word ‘atheism’ unnecessary in some/most situations, that does not mean that all people find that word unnecessary in all situations. That word is very much necessary, I would say, albeit not everyone has to use it if they, personally, do not need to or if they do not want to.