I'm not sure why not collecting stamps would be considered an act.Could be any number of things - but collecting or not collecting stamps is an act - atheism is not.
In any case, if you want to see things from my perspective, imagine an avid stamp collector asking you what meaning you get from not collecting stamps or what purpose not collecting stamps serves. You asking about atheism comes off like this to me.
Your god may be the centre of your worldview, but to me, the question of whether your god - or any god - exists just isn't that important.
Don't get me wrong: religion imposes itself on society in all sorts of ways that I care about quite a bit, and I find theism and religion interesting as social phenomena, but I don't really care about your god.