Spot on 
That's why professional fence sitters (also known as agnostics) like myself keep an open mind about the existence of some kind of omnipotent being, or an afterlife. As soon as there is some kind of evidence to support it, we'll quite happily change our minds.
On the other hand, believing in something despite piles of evidence to the contrary (Earth is 6000 years old, intelligent design, etc) is just idiotic. Or, 'faith', if you prefer that term.
Agnosticism addresses knowledge ('knowledge that', rather than 'knowledge of', which is awarness of a concept). Theism addresses belief, specifically belief in a god or gods. These are two different questions.
Thus, you can have the following:
Theist gnostic - "I believe and I know that a god/gods exists"
Theist agnostic - "I believe a god exists, but I don't know if a god exists or not"
Atheist agnostic - "I don't believe a god exists, but I don't know if a god existis or not"
Atheist gnostic - "I don't believe and I know that no god/gods exists"
With theism, there are only two possibilities: either you believe, or you don't.
Think about a jar of coins. There is either an even or an odd number of coins in the jar, just two possibilities.
The theist position is one of a positive claim, such as: "There is an even number of coins in the jar". This is analogous to the claims "There is a god/gods".
The atheist response is one of skepticism. The response is: "No evidence has been given to support the claim that there is an even number of coins, therefore I don't believe it".
Note that this is not a positive claim. The atheist is not rejecting the possibility of there being an even number of coins ("A god existis"), nor are they asserting that there is an odd number of coins ("No god exisits"). All they are asserting is that the positive claim has not meet its burden of proof and been substantiated and thus they don't believe it.
