The Bible leaves out one key point. They didn't know better when they did it, did they?
From the Christian point of view, they did because Jehova had told them not to.
Evil, wrong, and sin, do not exist anyway. Nor does moral rightness or holiness.
Up until that point, there was no sin until the fruit was eaten but Evil and wrong were present in the form of the Snake and the temptation.
Nothing in the Bible actually happened, anyway. There is evidence disproving the flood, disproving the exodus from Egypt, and the geological record disproves the Genesis story wholly. Abiogenisis continues to show there was no prime mover.
The Bible needs to be understood from the language (Hebrew is a symbolic and highly metaphoric language) and times it was written in. The flood story is well documented in the form of the Gilgamesh flood story and in the archeological record from the Black Sea which was once an inland, fresh water lake until the sea broke through the very narrow entrance. As for the exodus, it may be a metaphoric story and Abiogenisis would not be a concept which early peoples would have any need to know or pass on. It doesn't make sense as a metaphoric story.
The bigger problem seems to be that fundamentalist Christians have taken the old testament literally which it was never meant to be.