The statement, “God does not exist,” is perfectly fine when used in normal conversation. Many atheists are heard saying this and they are attacked for it because of epistemological reasons. In the epistemological sense, this statement is not okay because it has not been proven that God does not exist. In fact, it may well be impossible to prove that God does not exist.
Likewise, the statement, “Santa Claus does not exist,” is perfectly fine in ordinary conversation but it’s not okay in an epistemological argument because it has not been proven in the strict sense of logic that Santa Claus does not exist.
When somebody says, “Santa Claus does not exist,” their statement is epistemologically suspect. But what the person really means is, “The available body of evidence does not warrant a belief in the existence of Santa Claus.” The latter statement is fine in the epistemological sense but the first statement is not. The first statement is fine in normal conversation because we are used to taking shortcuts in everyday language. It is the same way with the atheist’s proclamation that, “God does not exist.”
Before you rail on the atheist for making epistemologically suspect claims, perhaps you should consider what the atheist really meant. Before you claim that atheism is an untenable position because it asserts a nonexistence claim, perhaps you should consider what it really means.