The thing is, you're making this sound as though a believes x and b believes y and both x and y are equally likely.
Whereas in reality the situation is more like a believes x, b doesn't believe x and there is absolutely jo evidence for x.
Atheism is not a belief - it's in fact defined as a lack thereof. An atheist is a person who doesn't believe that a god exists. Now, note that some people will also actively belive that there is no god. However, this is not necessary to make someone an atheist and is, in fact, a belief that cannot be proven.
If people honestly believe that there is an equal burden of proof for those who do not believe in something, I am impatiently awaiting their essays on proofs that the classical goddess Ceres doesn't exist. If you're a pagan and have incorporated Ceres into your belief system, you are naturally exempted from this task.
Also, in terms of superiority and acceptance: as an atheist I have to accept people's religious beliefs in multiple contexts. FWIW, I am a dual national and cannot even sing one national anthem without it being full of references to the christian god ("Nobody save the queen", anyone?). Most of us have no issues with other people believing whatever the hell they want. It's just that as soon as you say that there is no god, someone will find it offensive or "sad". And then there is of course the fact that in the Abrahamic religions at least my lack of faith entitles me to a free spot at the eternal barbeque. I find that offensive, but to say it is full of shit would be insulting to someone's religion, right?