Though I agree with your feelings, you're incorrect in saying that
" The concept defies all reason. It makes no sense at all."
The argument is as follows:
I. Cause and effect must be obeyed.
II. The penalty for a perfect human is that perfect human gets life removed.
III. Adam sinned as a perfect human, therefore his perfect human life gets removed.
Meanwhile all the lil-life force decendent bags get blown up and righteously popped like so much bubble wrap until...
IV. Perfect life force chooses to enter in and seal off all the bags that popped with the value of its life force.
V. All the bubble-wrap gets fixed.
VI. Then the bubble-wrap that got fixed get the same test.
VII. Bubble-wrap that passes doesn't get popped.
It seems rather pointless to me, though. I'm still trying to make any sort of MORAL-sense out of this that corresponds to some uber-deity.