I can’t really justify the labels and definitions put on atheism, agnosticism, or any religion for that matter, as they of course are terms for spectrums of practices as varied as the individuals that practice them. As an example, my uncle lives in a town with a population of about 13,000 that has a dozen different Baptist congregations, no two of which probably agree on what “Baptist” means.
I would say that my understanding of the classic definitions of agnosticism, and my personal definition, is that “agnosticism” is derived from the Greek words “a,” meaning “without,” and “gnosticism,” meaning knowledge, and thus “agnosticism” is the belief that the answer to the question of whether a Divine Power exists is empirically unknowable. By that definition, I guess I’d have to call myself an agnostic, although I am a Christian, and as a matter of faith believe that God exists, however, I agree that this is purely an assertion of faith, and is incapable of empirical proof. That does not, however, make that belief false, any more than the inability of atheism to prove God does not exist proves atheism is false.
I do believe that there is quite a bit of what a lawyer would call circumstantial evidence that some Intelligent Power, not necessarily a Divine Power, in some manner either created the universe OR (not necessarily AND) currently controls its design and operation. That is not the same as saying God or any particular god exists now. It is that sort of evidence that is leading more and more formerly atheistic academics to conclude, through an application of the scientific method, that there was or is some Intelligent Design.
Atheism, since it asserts God does NOT exist, is as much a matter of faith as any religion, as it makes an assertion of the unprovable. Agnosticism, by saying the question is unknowable, in my opinion, does not make an assertion of faith, but is rather a statement of fact. Understand, however, that my definition of agnosticism inherently does not preclude belief in any religion, but rather recognizes that faith does not need proof.
I do find it amusing, and I hope God does as well, that Man has the presumption to think God needs to be proven. God either is or isn’t, and whatever God is, God is completely unaffected by our attempts to define God. If my God was small enough for me to understand, God wouldn’t be big enough to be the God I need.
There is a big difference between knowing what one believes and knowing what one knows. I don’t find agnosticism contradictory to religion at all. Just because I admit what I cannot know, does not mean I doubt what I believe. Perhaps the only way we could “know” God exists is to be divine ourselves, as perhaps our flawed minds cannot possibly conceive the concept of God.
For a great analogy (and a really good read) I recommend E.A. Abbott’s Flatland.