What "agnostic" and "atheist" mean
Much of the disagreement here is due to ambiguity and lack of precision in the language being used.
Atheist simply refers to anyone who doesn't believe that God exists. Some problems turn on the word "believe." Some atheists deny they are saying they *know* God doesn't exist, they simply believe God doesn't exist. Others don't like it when others point out that atheism is also a faith based belief.
In fact both have a point, but what an atheist can't claim is both formulations. If an atheist wants to claim rationality leads them to *know* God doesn't exist, then they are obliged to provide rational proof. If they merely want to say they *believe* God doesn't exist but can't prove it, then they have to acknowledge that there is some degree of faith beyond pure rationality involved.
In other words every atheist has a choice. They can either offer a proof or admit that their atheism is to some extent an article of faith. What they can't say is "I can't prove God doesn't exist, but I nevertheless know for sure he doesn't."
When it comes to agnostics there are two kinds, sometimes called hard-boiled and soft-boiled.
The hard-boiled agnostic says that not only do they not know whether God exists, they don't believe anyone else can know either.
The soft-boiled agnostic says that they don't know whether God exists, nor do they know whether it is even possible to know one way or the other.
I embrace soft-boiled agnosticism. It seems to me that if God as posited did exist, that God by definition could see to it that individuals *know* that he exists. In other words, if God exists then divine revelation must be a possibility.
I don't think the hard-boiled agnostic has a reasonable response to the observation that if they don't know whether God exists or not, they also can't know whether divine revelation is possible or not.