Technically, you make a point. For practical purposes, though, "atheism" makes sense in the world we live in...because it is a world dominated by religions and 'believers'. It would seem that the 'burden of proof', unfairly, lies on the 'unbelievers' in much of society...
There almost seems to be no room for neutral. Most of humanity is born into a pool of one god-belief system or another...and we either learn to absorb it and swim in it...or we shed the thinking and become a minority, or an "a"thiest. If the world were neutral on the subject, or 'nonbelievers' were the majority, I believe people wouldn't be as inclined to call themselves "anti" or "a".... anything
So, my opinion is that using the word 'athiesm' is appropriate, in this backwards, religious/god dominated world...it helps people put into context the person's beliefs. It is a quick way to describe that a person doesn't believe like most, that is, in a sky daddy of some sort.
Ideally, a person wouldn't have to explain that they don't believe in an unproven 'god'...we just aren't there...yet, anyway...