But the idea of original sin is essentially a way of explaining what Pruni was talking about earlier -- the tendency of the best human ventures to go belly up because, in the end, we all fall short of the best that we could be.
The essence of Christianity is that, although we are all less than we might be (because of human weakness, sin, call it what you wish), we are nonetheless forgiven and accepted. That forgiveness is offered to us; we are not forced to take it. But if we choose to reject it, we are turning our backs on the chance to be the person we are called to become.
Coming back to CS Lewis, I like the scene in the Last Battle where the renegade Dwarfs are all sitting around in what they believe is a stinking stable surrounded by filth and dirt. However many times the others describe the beautiful fields and surroundings, the Dwarfs have so blinded themselves to what is good, that they have rendered themselves unable to respond to it.
As regards followers of other faiths being damned, I was told in no uncertain terms when I raised just this question in first communion classes: 'We know where god is; it is not for us to judge where he is not'.