Right on - now we're finding the common ground!

Yes, I also take the optimistic view. We've not lost our original nature at all, its still there, "beneath the veneer".

"So the "loss" isn't an absolute one. To me that's different from a true fall."

Having fallen doesn't mean that you can't climb back up. Loss doesn't imply no possibility of recovery. To make that implication the word "loss" must be strengthened with "irrecoverable".

Having said that, though: in the Bible the entrance to Eden, once Adam and Eve have been kicked out, is guarded by some angel dude with a whirling sword who is to prevent them ever re-entering. In many ways this is true, psychologically speaking. We have now developed the faculty that distinguishes us from the animals and it is neither possible nor desirable for us to undevelop it. So we can never truly return to what we once were. But we <i>can</i> get back in touch with the parts of what we once were that currently lie dormant, and integrate them with our reason. This, surely, is the way ahead for humanity's psychological development?