I agree that it is philosophically improper to label a non-belief
Why? Labels are just conveniences - it saves us saying "I don't believe in the existence of god or gods". It's fewer words.
I agree that it is more convenient and we should still use it so long as theism is the norm, but...
it is philosophically improper, because in philosophy if we were to label every non-belief we would have to label an infinite number of things, like non-astrologers, non-racists, etc. So in order to be philosophically proper, a label must represent a belief, rather then a non-belief.
I am not saying that we should always be philosophically proper as it it would get tiresome if instead of saying atheist you said "those who don't believe in God."
Just a note*All people in my view are born atheists, or rather more correctly they are born with absolutely no beliefs, then they are indoctrinated etc... however, it would be better if all people started from a point of absolute ignorance and worked their way up, sort of like what Descartes did. When I did this philosophical exercise I was able to form a unified hypothesis of the world, which I think is pretty reasonable. Though my hypothesis is undoubtedly untrue, it is my best guess, but more to the point is that the exercise made me realize what beliefs I held without any support and those that I should hold because they stand on greater ground. If you haven't tried it, I think its a good exercise for anyone who wants to test their own belief system, not just philosophers.