I say that I’m a strong atheist for the exact reasons you mentionned in your OP. There are plenty of things I don’t have any reason to believe in and don’t believe in them, and I’m never called on them. Why? Because the overwhelming majority of people don’t believe in them, either.
But for some reason, when god is involved (or more exactly when current religions are involved… essentially nobody would tell me I shouldn’t rule out the possibility that Osiris and Quetzalcoatl actually exist), I’m supposed to be more cautious, to be a “weak atheist” or some some sort of “agnostic”, and, though I don’t believe in him, not to exclude the possibility that god might exist.
My answer is always the same : then, should I also apply the principle to all beings I believe don’t exist : ancient polytheist gods, djinns in a bottle, unicorns, etc…, to all things that are believed by some people (for instance, what’s the proof that one of my friend is actually schizophrenic? Perhaps the military is really spying on his brainwaves and some TV programms are reallly broadcasted just in order to send him messages), and even to all things nobody believes in but can’t be disproven (trees are actually sentient beings, they unroot, wander around and discuss with each other in loud voices when nobody’s around).
So, yes, I definitely say “There’s no god” rather than “I don’t believe there’s a god” because I’ve no reason altogether to believe in such a thing, because essentially everybody is a “strong non-believer” in plenty of things and nobody thinks it’s worth a debate, essentially nobody would say one can’t exclude the possibility that unicorns actually exist and I’ve no particular reason to treat god a different way.
IMO, either you state that plenty of things, including god don’t exist, either you doubt about everything, even the most crazy and unheard of concepts and beliefs. Yes, it’s theorically possible that god exist. It’s simply not worth mentionning because it’s similarily theorically possible that my tree gatherings at night actually take place (and don’t try saying that contrarily to god, one can observe trees and disprove this theory, it’s impossible. Not only they’re very clever, but also I’m allowed to come up with plenty of supernatural or “magical” explanations for everything…I’m even allowed to “unknowable mysteries” if need be).
I would even go so far as telling that a significant part of the weak atheist or agnostics are actually “weak believers” who aren’t sure whether they should believe or not. Simply because if they were actually following a general and logical reasonning, they would apply the same principle to every kind of belief, and, in their overwhelming majority, they don’t. They might tell you “I believe there’s no god, but nobody can know for sure”, but won’t tell you the same thing about fairies. From that, I conclude they aren’t actually using a rational and consistent system of thought, but rather are unwilling to reject a particular belief in a particular supernatural entity.