I've always found this one;
The explanation is to demonstrate once and for all Jehovah's right to rule. Man has been given time to demonstrate the ability to rule. How good of a job has he done?
.. to be a bit suspect.
God; "Okay Mr. Smarty Human, you think you can rule yourself. Go on then, see what happens!"
Man; "Okay."
God; "Oh, but you're gonna be suseptable to disease and will die."
Man; "How's that fair?"
God; "Fair? What's fair got to do with it?"
Man; "Well, I was perfect, and decided to rule myself, now you're gonna let me prove it BUT without perfection - you're setting me up to fail!"
A few generations later and God, having siad he'd let man rule themselves to show how incapable they are, interferes and kills off everyone but Noah and his family. Despite this terrorism against and destabilisation of man rule, a few generations later men get their act together and build Babel.
Man One; "Hah, well, despite the fact we now age and die and catch diseases we're still co-operating together succesfully".
God "Little sods - no telling what they might do - "abracadabra"!"
Man One; "Mag ik de hammer alstublijf?"
Man Two; "Eh, what did you say?"
Man Three; " ? ? "
Essentially the Borg's view of man's fall makes god a cheat; he takes man's actions as a challange, accepts the challenge, and then changes the rules the challange was made under so as to prevent the challange being succesful, and then, when it looks like his first lot of cheating wasn;t enough to win the game, cheats again.
If man were still 'perfect', then the ability to govern themselves would be vastly enhanced. Monkies with an 80 year life span make poorer decisons than humans with infinate lifespans; they learn less, achieve less, cannot build on their achievements as they die.
If god had played fair, Adam and his descendents would be giving god the finger from more than one solar system by now.