Why Agnosticism?

[Ace Otana]

However, even on this definition, if you do not know whether God exists or not then there is no firm basis for rejecting the idea and, therefore, the act of rejecting must be based upon an act of faith.

You don't need any knowledge or understanding to lack belief in something. We all lacked belief in god from birth. Babies are too young to understand and take things on faith, yet they lacking of belief in god (according to you) is faith-based?

You lack belief in Santa do you not? Would you also say that lacking belief in Santa Claus is also faith-based?
I lack belief in god due to lack of evidence and credibility. I do not believe in god. I really don't think that such a being exists, but at the same time, I don't claim to know that there isn't such a thing. I just can't bring myself to believe in it.

Science often rejects claims, it doesn't do this with faith. If you claimed there were pink elephants hiding under the moons surface, this claim will be rejected unless you can support the claim.
Theists make the claim that a god or gods exist but fail to support such claims. So I reject their claims as nothing more than baseless assertions. Rejecting the claim that a god exists is not faith-based.
Do you not reject tooth fairies? Do you not reject magical pixies? Do you not reject magical flying rabbits?
We don't need absolute knowledge to reject an idea or claim.

believing that God does not exist.

The word 'believing' doesn't fit my position. I lack belief. How can one believe in lack of belief in X?
I have no belief when it comes to religion. Only lack there of.

You don't need faith to lack belief in anything. Unless you can point out where the whole faith thing comes in? From birth I was an atheist, so when in my life did I unknowingly took a leap of faith?