Imagine asking one scientist (Scientist A) "Which theory do you support: Neo-Darwinism or Creationism," and the scientist said he had not come to a conclusion.
Then imagine asking another scientist (Scientist B) the same question, but she answers "The question makes no sense. Neither Neo-Darwinism nor Creationism is a scientific theory. They are historical reconstructions. Science describes how the universe in general works, not what may or may not have happened on this particular rock. We call that branch of knowledge 'history.'"
Would you consider these two answers similar?
Now, imagine asking someone (we'll call her Jessica) "Jessica, do you believe in God?" And Jessica answers "Well, I read The Case for Christ and Evidence that Demands a Verdict, but in the end I think we humans just cannot know about God or if there is one...regardless of what we might have as evidence."
Now, imagine asking someone else (will call him Kevin) "Kevin, do you believe in God?" and Kevin answers. "I haven't decided what I believe." And then you ask him what he has done to investigate the question, and he says he hasn't really done anything. He has more important things to do.
Would you consider these answers similar? I wouldn't.
People use the term "Agnostic" to refer to a wide variety of belief holdings. I personally think people who are "undecided" like to call themselves "Agnostic" because it makes them feel more complete...it lets them "fill out their profile" with something other than a question mark.
The problem is that there is already a perfectly good word for not personally having made up your mind [or not personally caring one way or the other], which is the state that many are in. We already have the term "undecided."
We don't have another good word for someone who has had a more serious introspective dialogue and come to the conclusion that such things are not knowable.
Another problem is that adhering to a religion, or even claiming the theology of atheism (which is not a religion), at least is a claim. It means affirming something. Saying you are "agnostic" in the sense of "we cannot know" is also at least a philosophical affirmation, but saying "agnostic" when you really just haven't figured it out yourself, and perhaps don't care to, is not a claim about anything.
What do you think Agnostic should mean? If people use "Agnostic" to mean "undecided," then what should we use to mean "no one can know"? We could use the terms "Strong Agnostic" and "Weak agnostic," but that seems a rather unfortunate option...especially since one says nothing at all and the other says something profound about epistemology.