Earlier quoted context omitted.
Depends on your precise definition. Most atheists consider atheism the lack of belief in a god, as opposed to the belief that there is no god. The distinction is important.
Most people I know who claim to be atheists seem to believe there is not god, despite not being able to prove it. Agnostics seem to be the most honest ones....
For example, many people are vegetarian for one subjective reason or another. Just because I'm not vegetarian doesn't mean I believe being vegetarian is wrong or isn't a thing -- it just means I like eating meat and don't have the same reasons as vegetarians to subscribe to vegetarianism. And I don't think about vegetarianism, like how some atheists don't think about god; this stands in contrast with those who subscribe to religion, which requires active belief / prayer / practice / absorption of certain ideals into your identity.