Indeed, how else would you categorize atheists? A lack of belief in God is basically the only thing that can be definitively said about them, since there exists no central tenet or dogma beyond that which links atheists together. I'm relatively sure it's not only an acceptable way to describe atheists, but perhaps the only accurate way to describe them.
Of course it's not a complete description of a person who is an atheist, as Mister rightly stated. There's always more to a person's personal philosophy. But at that point, it's just that: a person's personal worldview or philosophy. You will learn more about the individual, but not about "atheism" in an abstract sense.
Mister, you're just looking at labels the wrong way. It doesn't strip away individuality, it provides a useful tool for shared meaning in society. We frankly don't have time to go into our worldviews in most religious discussions, so terms like Christian, Episcopalian, Atheist, Jewish, etc. are handy tools to form a basis of knowledge. Nobody pretends that they represent everything about a person. Abhorring convenient descriptions is just ignorance of their function. But, and here's your other mistake, when you say "Catholic" for instance, it refers to a gigantic set of beliefs and tenets. "Atheist" doesn't. It refers only to a lack of belief in a god or gods. So saying that atheism is much more than that is false. People are more than that, atheism is not.
Frankly though, this discussion might be better served in the general atheism thread now, because the premise of this thread as it was created remains embarassingly clueless.