Not necessarily without evidence.
That also applies to Santa, the tooth fairy, and the Greek gods. The point is, they don't need to be disproved to not be believed in; they need to be evidenced for there to be a reason to believe in them. Existential negatives are assumed until positives are evidenced. It's the rational way to live--do the opposite, and you'll immediately have to make an infinite number of assumptions, many of them mutually exclusive.
But there is proof to the non existance of Santa and the Tooth Fairy. Someone (ie parents) have admitted to, well, faking them. And people have claimed to have had been effected by God, either through manifistation, or miricles or such like. To them, they have proof, just not a proof they can show us.
From what you are saying, a thiest says 'I will believe without proof", which is irrational (but then spirituality is not normally rational). An Athiest says "In the absence of proof for the existance of God, I will assume there is no God", while an agnostic says "I have no proof for or against the existance of God, therefore I will not take a position either way." To me, that makes the most sense of all. And before you ask, I have an agnostic viewpoint to anything I cannot prove or disprove, including Greek gods, Norse gods, celtic gods, Hindu gods or any other. I had an agnostic view to Black Holes, till they found one.
I never said theism implies practice. Religion implies practice. A religion is a belief system.
I would be interested in your view of Buddism, given it's lack of gods.
It is one of the things Lini is for, taking the blame. She usualy deserves it even if I don't know how.