We all accept those propositions, as without them, as you said, we'd reach a dead end. And we all agree on that being a reason for why it's reasonable to hold those beliefs.

The problem is when you require a belief of something much less reasonable. And that's what atheism refuses to do.

Atheism is more about admitting to not know, so I'd argue it doesn't need a proof. By accepting it, you are not accepting any additional information into your belief system. You just refuse to accept some specific ones.

It's like - if you say you don't accept the fact that the Earth is round, you are not saying it isn't round. So, a person that accepts it is round, in fact is more likely to be wrong. It's specific claims of knowledge that require proof (or evidence).

I think it's a fault of our language that we can only express belief and disbelief. Not accepting something seemed to be unnecessary in the course of our evolution.