The concept of 'original sin' in many ways isn't a much discussed topic anymore - at least in the part of the Christian world where I come from. It has become a somewhat faded aspect of Christian theology and spirituality, I guess for a big part because of some obvious aberrations like the idea that babies would be damned to hell if they weren't baptised in time. Nonetheless, when properly understood, the spiritual idea behind the concept of original sin can be of much worth to people's understanding of Christianity.
Carl Jung once said: "When one lives one's own life, one must take mistakes into the bargain; life would not be complete without them." There is little counterargument to such a statement. Everyone is indeed inevitably confronted with pain, problems and mistakes in his or her life. Perhaps it might theoretically be possible to live life without making mistakes, but in all factuality of life, humans simply make mistakes. It's a spiritual fact we better take for granted.
So 'original sin' doesn't say anything about innocent babies but it refers to the vulnerable human condition we all find ourselves in. 'The fall of Adam' is a symbol for the fact that somewhere along the evolution of the human race, we developed 'ego' - that is to say, egocentrism and egoism - and as we have all experienced ourselves, this self-centered ego is inclined to sin – that is to say, it often choses to do things that directly or indirectly hurt people, including ourselves. It has simply become a part of our human constitution and we have to learn to deal with it.
One way of learning to deal with it is by realising that because of our stuckness in ego, we will always be in dire need of grace. For our own egos can't untangle themselves. They are, after all, their own problem. So by definition we need to be pulled out of them. The divine hand needs to be mercifully stretched out to us to pull us out of the merely human condition and into a state of deeper 'soulfulness'.
We can however look at the concept of original sin in yet another way: as the burden which is carried along through the generations. For many people it seems a bit bizarre that we should have to 'pay for the sins of our forefathers'. But, whether we want it or not, in a way, we inevitably do. Not even as a spiritual idea, but as a matter of fact since it is difficult to deny that the human race, for a long time now, disrupted many God-given balances of human society as well as the world at large. Worldwide economic disparity and the global ecological crisis are the most prominent examples thereof.
Of course, these imbalances are not strictly speaking the 'sin' or 'fault' of any particular generation but the sad reality is that we also can't get rid of the 'collective burden' of these imbalances. Even more so, they aren't just a burden, they're also a constant moral question because the way all of us personally choose to live, will determine whether we perpetuate these imbalances or slowly try to solve them.
The importance of the message of Christ, then, is the idea and teaching that this 'original sin' of a self-centered ego and the imbalances produced by the collective self-centered egos isn't the final word. Christ's life and message show that there are ways out of it. So the message of original sin isn't that we're doomed, but quite the reverse: that there is a way out of the perpetual mistakes of the human condition. For Christ's example shows that the ego can be transcended and that the balance between God and the world can be restored.