So when we assume all of this, it is then obvious that evil did not come into the world when Adam and Eve ate the fruit, but when the epitome of evil arrived here. Shouldn't it be then that the world was tainted?
God commanded Adam and Eve, who at this point have no clue about good and evil to follow a command. This one command, don't eat that fruit... don't even touch it... I'd prefer you don't even look at it... on second thought, don't even think about it. Adam and Eve, being innocent and curious creatures naturally gravitated toward the fruit.
The only thing which stands between them and the fruit is God's threat. One which seems unfounded without an innate sense of morality. God never told them that to eat the fruit is immoral, and if he did they'd need to have a foundational knowledge of morality. That defeats the purpose.
So with a dogmatic command to heed, the pair were blissfully ignorant of any moral issue. The serpent presumably knew this and exploited it to it's fullest. He made a counter-offer to God's threat and Adam and Eve took it. They ate the fruit, breaking only an unfounded command. After that all hell (all too literally) broke loose on the earth and the omnescient God who created and planned it all was dismayed.