More recently, atheists have argued that atheism only denotes a lack of theistic belief, rather than the active denial or claims of certainty it is often associated with.
I'm having a hard time seeing what point there could be in arguing that "atheism only denotes a lack of theistic belief." Note first that atheism cannot be identified with the lack of theistic belief, i.e., the mere absence of the belief that God exists, for that would imply that cabbages and tire irons are atheists. Note second that it won't do to say that atheism is the lack of theistic belief in persons, for there are persons incapable of forming beliefs. Charitably interpreted, then, the idea must be that atheism is the lack of theistic belief in persons capable of forming and maintaining beliefs.
But this cannot be right either, and for a very simple reason. Atheism is something people discuss, debate, argue for, argue against, draw conclusions from, believe, disbelieve, entertain, and so on. Atheism, in other words, is a PROPOSITION: it is something that can be either true or false, that can be the object of such propositional attitudes as belief and disbelief, and can stand in such logical relations to other propositions as entailment, consistency, and inconsistency. But one cannot discuss, debate, argue for, . . . believe, etc. a lack of something. Atheism redefined as the lack of theistic belief is a PROPERTY of certain persons. Now a proposition is not a property. Atheism is a proposition and for this reason cannot be redefined as a property.
Someone who understands this might nevertheless maintain that 'negative atheism' is a proposition, namely, the proposition that there are people capable of forming and maintaining beliefs who simply lack the belief that God exists. Admittedly, one could use 'atheism' as the label for the proposition that there are such people. But then atheism so defined would be trivially true. After all, no one denies that there are people capable of beliefs who lack the belief that God exists. Furthermore, if 'atheism' is so defined, then theism would be the view that there are persons capable of belief who have the belief that God exists. But then theism, too, would be trivially true. And if both are true, then they cannot be logical contradictories of each other as they must be if the terms are to mean anything useful.
Now what is the point of the terminological mischief perpetrated by these 'negative atheists'? It is terminological mischief because we have just seen it ruin two perfectly good words, 'atheism' and 'theism.' If atheism and theism are worth discussing, then atheism is the view that God does not exist and theism is the view that God does exist. ((I am assuming that by 'God' we understand that being who is the main target of the venom of militant atheists, namely, the God of the Abrahamic religions. We are not talking about Spinoza's deus sive natura or anything of that order.)
Consider the parallel case of a nominalist who for whatever reason does not want to be taken to be asserting any positive thesis. So instead of adhering to the standard understanding of 'nominalism' according to which it is the view that there are no universals and that particulars alone exist, he proposes to redefine 'nominalism' as the absence of the belief that there are universals.
But now the same problems arise. One cannot argue for or against nominalism if it is merely a lack of belief. And if you say that nominalism is the proposition that some people lack the belief in universals then that is true, but not worth arguing for or against. One does not argue for or against a trivially true thesis that all accept.
So what's going on here?