I believe that how a person structures his spiritual belief system has more to do with where they were born and where they live than any kind of spiritual calling. If this DB was created in China or India the discussions would be similar but the mythical religious figures we talk about would be different.
I think you are absolutely correct. I identify myself as a Christian because I can still use the core elements from the Christian storybook as a touchstone to define all of my remaining beliefs in spirituality. Under different circumstances, I might be going on about elements in some other religion which I would pick and choose to provide a viable spiritual structure. But for now, for myself and amongst most of my neighbors, Christianity still provides the most immediate framework to help categorize new spiritual ideas as to whether they are already a part of my defined spirituality, or if they can be subsumed within it, or if they are unworthy in comparison or are, perhaps, superior to it. It's much the same way a person might describe themselves as a Keynesian economist amidst a current playing field of economic permutations that can never again allow an ideal Keynesian system. Yet analogies based on Keynes in the context of systems of his time can also provide valuable analogies for comparison among systems that hadn't even been tried in his day.
The thought that we were all born in sin keeps the meek, humble and gullible in line. We all have the ability to know what is right and wrong. Blaming Satan for things you do wrong or thanking god for things you do right keeps people from realizing the personal potential and self worth. Eliminating ones self worth and independence is the key to religious control. Own their minds and their bodies will follow.
This gets right to the point of the thread title. However, I think there are other lessons in the Christian story that are much more important than a teaching that we are "born in sin." My earlier examples from John and Luke about whether it was sin that made the boy born blind, or sin that caused the tower to fall and kill some people, tells me that this idea must not have been a core part of Jesus' teaching. I am a literalist when I read the story, and if some ideas from later apostles have proved literally wrong, then that's part of the "moral of the story." They were simply wrong!
I agree that Paul tried to promote a version of the ransom story, for example. But he premised it (I don't know why, exactly) on the idea that Jesus had literally been resurrected, that if the resurrection didn't happen, then we are without hope in the world. Then he stuck his neck out and spoke of what that hope entailed (rapture, last days, imminent judgment day, etc.). It didn't happen. But the core of Jesus teaching wasn't premised on a ransom. The core of Jesus teaching was what Paul had to admit: that faith can fail, that hope (resurrection?) can fail -- but love never fails. Love is the purest motivator of spirituality. Put another way, as James said: "the purest form of religion is to look after suffering orphans and widows." For others, of course, that love will motivate different activities -- but as a system of spirituality, the "love motivation" is the remaining core of Christianity.
Sorry for the sermon, but I think the real, core lessons from the Christian story are very empowering. I doubt my "twisted" version of Christianity has much chance of catching on, but I have faith that if it (or something like it) did catch on, then ultimately, love (for our neighbor) can motivate against militaristic/corporate greed, for example, and thereby help extend the life of the planet as a home. It could promote the creation of medicine and healing practices that reduce pain and suffering -- so I also see salvation in this teaching. You are right that we don't have to call it Christianity -- but that's where I happened to find this teaching.