However, atheism by definition is not someone who doesn't believe in something. Atheism, in a narrow sense is specifically the position that there are no deities.
I would agree that a majority of atheists are not sitting on the fence as to the existence of a deity. Atheists have been waiting since the dawn of time for theists to present us evidence that their gods exist. None has been presented. So we don't expect that there is a god, and for good reason. However, we don't have an absolute belief that there are no gods. If Zeus appeared in front of me I would certainly be surprised, and I certainly wouldn't be expecting it. However, I would absolutely accept that Zeus exists.
If I took a cube, and pulled a perfect vacuum on it, I could easily prove with 99.99% certainty that there is nothing material inside of it. If you said to me, there was a god inside of it, I would have no way of detecting that god, since we cannot detect things that do not exist in our dimension, or however gods exist, so I would have to take it on faith that there is nothing there, because I believe there is nothing there.
That is not analogous to the atheist position. We say that no one has detected God. Therefore, there is no compelling reason to believe that God does exist. Could there be a God? Sure, but we really don't expect God to exist given the absence of any detectable evidence for the existence of God. This doesn't require faith to state that there is no evidence for the existence of God.
To go back to your cube analogy, it doesn't take faith to claim that there are no known tests that detected anything in the cube, God or otherwise. We would then ask what evidence the theist had for claiming that God is in the cube. After the theist is incapable of coming up with the evidence we are back at square one, no evidence for God. There we sit, waiting for evidence of God.
A true scientifically minded person, or logically minded person would never be an atheist. He would always leave room open for further interpretation. At best he would be agnostic.
A true scientifically minded person, or logically minded person, would never assert that a being exists for which there is no evidence. Therefore, they would be an atheist.