I get that the gnostic/agnostic distinction serves as epistemic shorthand when describing your flavor of atheism, but is a spurious distinction. Let me explain.
Some people call themselves gnostic atheists in order to indicate that they know with certainty that gods don’t exist. Others use agnostic atheist to indicate that they don’t believe gods exist but they can’t be absolutely certain. It’s a distinction without a difference. That’s because being an atheist is an epistemological position, not an ontological one.
However one parses the definition of atheist, it is all about non-belief. It’s all about rejecting the proposition that gods exist. Belief is a necessary condition for knowledge. Think about how many times you’ve gotten into a debate with a creationist. Their disbelief always prevents them from knowing evolution. I should note, that belief is necessary, but on its own, insufficient for knowledge. I could deliver a graduate course in epistemology here, but suffice it to say that belief doesn’t disappear from any current account of knowledge (except for skepticism which says knowledge is impossible).
Still, objects exist entirely independent from one’s knowledge of them. As humans, we engender relationships with objects of the universe through our epistemological enterprises: science, philosophy, art, etc. But these objects are not contingent upon there being humans in the universe.
Simply because the universe must be such that we can exist, doesn’t mean that we must exist. When we talk about the universe, nowhere in its formulation are humans (or even sentience) required of its existence. That is, unless you hold to the strong anthropic principle. In which case, you’re probably a theist.
To put some meat on the bones of what I’m saying, let’s talk about the weirdness of quantum phenomena. Quantum theory states that an electron can exist in two places at the same time. But based on the law of non-contradiction, this is impossible. Yet, it happens all the time according to observations. Does this speak more about the limitations of human knowledge or the laws of logic? I propose it speaks more to the former, though I won’t entirely rule out the latter.
We simply don’t know enough about quantum phenomena to know how to explain them without the apparent contradiction. When we discover more, we may be able to demonstrate the non-contradiction. This speaks more to the limitations our knowledge than it does to the universe itself.
The problem that the gnostic/agnostic distinction speaks to is that the universe is such that gods can exist. There is no law of physics or science that prevents the universe from having gods, at least for the time being. But when one honestly considers the evidence it’s so unlikely as to be virtually impossible. So when one says “I don’t believe in gods.” What are they really saying?
That they’re an atheist. Belief is entirely epistemological. So even if they say they know gods don’t exist, how does that matter? The belief is in there still. At worst, they’ve overstated their position. Who hasn’t? Let’s leave agnosticism to describe someone who isn’t committed to either side of the existential question. The agnostic/gnostic distinction is spurious. If you’re an atheist, you’re more sure than not that gods don’t exist. That’s all that matters.