Atheism is an affirmation
Wrong, it's lack of belief in gods.
of the non-existence of God.
Wrong. It addresses all gods, not just your particular one.
It is not a lack of belief
That's ALL it is.
as a mere lack of something wouldn't constitute a stance.
Which is why atheism isn't a stance.
The recent cowardice of the atheist position, defining itself into a kind of agnosticism
Agnosticism deals with making statements, not with belief.
rather than an affirmative statement is kind of off-putting.
Boo hoo. Do you really think we care whether you're put off by our lack of belief?
We define what we are. You get to accept that definition or you get to look like a fool who wants so desperately to 'win' that he has to redefine words.
I understand why it's done
Then why this post, that declares that you don't?
Atheism is typically supported by way of a materialist/naturalistic view of the world.
Atheism is solely "supported" by "I don't believe in any gods". It's the theistic stance that requires support, not the refusal to accept it. All seemingly nonsensical stances that are presented without evidence are rejected - by default. Religion is just one such.
So then you agree that the Christian God could exist?
Some god, depending on your definition of the word, might exist. But a god that's defined as to be self-contradictory, or impossible? No, such a god can't exist. (And the Christian god is both.)
Since you simply lack that particular belief, it's still possible that He exists? You just lack the belief that He exists for your various reasons. Is that right?
No, for only 2 reasons, basically. 1) There's never been any objective evidence that any god has ever objectively existed and 2) there's no need for any god for any reason.
But if some god did exist it would be a pretty trivial one. (For example, it's not possible for an entity that exists to create all that exists, if that's one of the properties of your god. Either the god can't exist or it couldn't have created everything that does. Or you're into special pleading, which is merely a convoluted way of tipping your king over.)