The problem for the Church is that science is slowly undermining belief even if not intending to. Original sin is a very important proposition to Catholics. Evolution displacing a God who created the first human couple leaves little room for original sin. The convoluted articles by Catholic writers to be found on the internet show how difficult it has become for the Catholic Church.
If the human race descended from previous near human forms where would a single couple, Adam and Eve, fit in? Did a few thousand people all commit the same sin? As far as I can tell (the articles are difficult to fathom) all of us descended from a couple who were originally part of a group. They received souls as did all their decendents. Presumably the unsouled all died out.
An admission that there is no such thing as original sin leaves the Church with it's heroes Jesus and Mary as not being immaculate after all.
Quite frankly it is much easier being an atheist only having to follow real evidence and logical thinking without having to take beliefs or wishful thinking into account.
All of the debates about whether the Bible should be read as referring to literal days, figurative days, or as simply being irrelevant are masking the real problems which evolution and the great age of the earth pose for Christians. If evolution is true, then a literal Fall from Grace in the Garden of Eden is not true — something which is obviously a problem for anyone who reads the Bible literally. Christians have, for a long time, accepted such metaphorical readings — thus it’s not an insurmountable problem.
If there was only a metaphorical Fall, though, why do we need a literal salvation? Perhaps a metaphorical salvation is sufficient? Some Christians may be able to take this step, but even those who read Genesis metaphorically will have trouble reading the Gospels as metaphors. This is, perhaps, not an entirely insurmountable problem, but it would be very close to one for many Christians. It seems that Christians need to see the Fall as not being entirely metaphorical in order for the atonement to be retained as literal.
Regardless of what sort of tales the Bible may contain, the fact is there was no literal Adam and Eve, there was no Garden of Eden, and there was no "Fall from Grace." The idea of "original sin" has no naturalistic basis and no relevance whatsoever to the development of our species. As there was no literal Fall from Grace, there is no need for a literal Salvation or Atonement — certainly no need for any literal sacrifice from a literal son of a literal god.
The entire body of Christian mythology is based on a foundation of falsehood; once the notion of original sin is removed it all comes crumbling down. There is no original sin to repent for, no sinful nature to feel guilty about, and no reason to seek out a savior to make sacrifices on our behalf.