My motive is clarity of language.
You've rendered a term essentially meaningless. How is that clarity? By your definition, rocks and unicorns are atheists.
I've found that the definitions of "atheist" that exclude babies tend to be either transparently arbitrary or logically unviable
Atheists are those that disbelieve in a god or gods. How is that 'logically unviable"? If atheism were a "lack of belief" in god then cats are atheists.
And I've found that most of the time, ulterior motives work in the other direction: it seems to me that when people object to the term "atheist".
I'm not talking about the rejection of the term "atheist" but the denial that atheism is a belief statement.
Something as good as a baby can't be something as bad as an atheist
That would qualify as an ulterior motive. Not one I've ever encountered but I don't doubt you have.
And agnosticism, especially the way Huxley defined it, would be beyond the capability of a baby
DING DING DING! Exactly. So is theism and atheism. They are all belief statements.
You don't need to have a clear definition of "god" if you define atheism in terms of lack of belief.
You don't need a clear definition regardless. Arguably, we don't have "clear definitions" for just about anything and we certainly don't for a great many things debated. The definition of words like "theory", "science", "mathematics", "religion", etc., are hotly contested and have been debated for decades or even centuries. The idea that clear definitions are even possible is disputed. A "lack of belief" requires a clear definition of belief which is again a much disputed issue (are all statements that belong to the linguistic realms of evidential modality, epistemic modality, mental state predicates, etc., beliefs?). This is just a cop-out, usually not deliberately but nonetheless indefensible. Do you really understand what photons and electrons are? No. Can you say therefore you lack a belief in them? Not honestly.
Generally, if I can't even conceive of a thing, then I can be sure that I haven't accepted that the thing is grounded in reality.
If I tell you that stars are made by the alien species Quasars, do you really need to conceive of these species in order to say it isn't grounded in reality?
However, if you define atheism in terms of rejection of belief
Then you get disbelief. That's what rejection entails. If, when asked whether or not I believe in unicorns, I reject the notion I'm not saying "I lack any belief on the matter" I'm saying they don't exist.
"Do you believe that ESP exists?"
"I reject that belief."
"So you don't believe it does?"
"I didn't say that. By reject belief I mean I don't have a clear conception of what ESP is and I lack a belief on the matter."
"Ok, but do you believe that 1st century Sepphoris was much less Urban than argued by prominent scholars 10+ years ago?"
"I don't know, because I haven't studied this."
"So you lack a belief on it?"
"No, I just don't know. If I lacked a belief on it than I wouldn't have a clear picture, like they way I don't with god."
"But, if you don't know, doesn't that mean you don't have a belief"
"Look, a teapot orbiting the sun!"
And so on. You don't get anywhere by equating a rejection of belief with a lack of belief. If you can conceptualize the thing you reject enough to know you reject it, then you don't believe in it and you believe that it isn't so. It's a belief.
then we do need a clear picture of exactly what needs to be rejected.
So to disbelieve in ghosts, you need a clear picture. What about to not reject? Do you require a complete understanding of evolution in order to say you don't reject it? Do you have a complete picture of how the brain produces what we call consciousness and the mind (if you do, I'll give you all I have for it as this would make me the leader in my field)? If you don't (and you don't), then how can you say whether or not you believe that the mind isn't the product of the soul (which we don't have a clear picture of) but of the brain?
It's not an objection to theists having the upper hand; it's an appeal to rationality in language.
It's a fundamental misunderstanding of how lexemes and other linguistic constructions correspond to concepts which are inherently vague, fuzzy, and intersubjective. If they were clearly definable computers could process concepts and everybody would speak some form of formal logic.
A definition like "an atheist is a person who is not a theist" is perfectly straightforward and, IMO, matches how people use the term.
What is a theist? If it is a person who believes in a god or gods, then to say you are not a theist entails that you do not believe what a theist believes. However, if you don't have a clear picture of what the god or gods theists believe in is (maybe it's Donald Trump!), then you can't say you aren't a theist as you don't have a clear picture of what this entails. You just don't know if you are a theist.
OTOH, I've yet to see a definition using rejection of belief that matches how people actually use the term "atheist".
That's because usage varies. I've never worked on a project trying to define atheism for some study but I have done it with materialism and spirituality. Words are polysemous, but some words are more vague than others and it's a pain to try to come up with just a usable definition for empirical study. Just for fun, I looked into usage using the entries from the carefully balanced Corpus of Contemporary American usage, the British National Corpus, and just skimmed ever so slightly through almost 200,000 usages from Google's N-Gram data. I was actually going to try to put the list up somewhere but there's no point (unless someone is interested). To illustrate how usage is problematic for naïve lexicology, the following two lines were listed one after the other in the BNC:
"the agnostic doesn't know whether there's a God or not; the atheist knows there is not a God. "
"But Ayer represents what is probably more often the position of the atheist, namely that it simply makes no sense to talk of God"
Your use seems to be (at least close to) the 2nd, while I think the first better. But the
key to using usage isn't to simply say whether a word is used inconsistently. Theism is used inconsistently too. And the solution isn't to define it to be so meaningless that people who don't speak English (or at least are unfamiliar with the English word "god") are atheists because they lack a belief in a word they've never heard. And, again, if atheism isn't defined in relation to belief in (or a lack of belief in) what the English word might correspond to but to a concept that isn't specific to any language, then clearly we have enough of a concept of god to map lexemes between languages to correspond to this concept. If you can say of people who don't know what the English word "god" means that e.g., pagans croyaient en beaucoup de dieux to mean they believe in many gods, or can say that Nietzsche did not believe in god because he denied that there was ein Gott, then you have a clear enough picture of the concept.
The extreme effort that I've seen people go to in order to come up with contrived definitions makes me think that something else is going on
I'm sure you've come across this. It rarely makes sense to run to a dictionary but people do all the time and then often assert that one sense is somehow the "true" one. The real issue is that dictionaries reflect, not define. That's why it's better to look not just at a dictionary but usage and especially (when possible) usage among specialists who have to take care when using terms that concern important aspects of their fields. Here, the issue is simpler. Stating that atheism is a lack of a belief in god rather than disbelieve or a denial of god (i.e., stating that atheism isn't itself a belief about the non-existence, or that an atheist isn't "someone who does not believe in the existence of a god"; WordNet) renders the term devoid of just about any meaning. Moreover, once can't reasonably defend the idea that atheism is nothing more than a lack of belief by denying atheists don't have a conception of what god is. If one is so truly incapable of understanding the concept that one can't say one doesn't believe in god anymore than
enekecheiron then atheism is simply sweeping and unparalleled ignorance. Atheism is anything but this, which is why I know that claiming atheists "lack any belief" in god(s) because, like theists, they don't have a clear picture isn't tenable.
It also has an "a" prefix. Just in terms of the structure of the word, it would work just as well to interpret "atheism" as "NOT the belief system of god(s)" as it would "the belief system of 'not god(s)'."
My point was let about the structure of the word
per se but that there's a reason the structure resembles theism, communism, agnosticism, environmentalism, activism, etc. When someone isn't a capitalist we don't call them acapitalist. We just say they aren't a capitalist. The reason that the Greek concept
atheos is no more but the word still exists in a different form is that it is conceived of as more than simply not being a theist.
Are babies not also non-smokers?
Possibly. But you are now describing an ability. That's different. Babies aren't runners because they cannot run. They aren't atheists or theists because they don't have the capacity to form beliefs about either doctrines or even understand the concepts.