I...don't need to fight you. It's not about burden of proof; it's about the definition of the word. Atheism is—as we agree—merely a yes/no classification of the belief in a deity; it is not a belief system in itself. As such, someone can be an atheist while still having a religion, which is a belief system, one that may or may not involve a deity.

Burden of proof only applies if one is making a claim in an objective context, not when one is making a claim in a subjective context.