"The problem isn't that they ate the fruit, it's that they disobeyed God." How would they know that disobeying your god is "wrong" without the knowledge of right and wrong, good and evil?
"They didn't know that eating the fruit was wrong, but they knew deviating from the instructions would be unacceptable." And how would they know that god-acceptance is a good thing, and god non-acceptance is a bad thing without the knowledge of good and evil, right and wrong?
"Well, they should have just obeyed God." Same problem – how do they know that obeying your god is "right" and not obeying your god is "wrong" without that knowledge?
"Because they should have listened to God and not the serpent." You're really not getting this. How would they know that listening to your god and ignoring the snake is the "right" thing to do? And why did this god warn them about the fruit, but not about the snake?
"Be… because it's written on everyone's hearts." So you're actually trying to say that people are born with the knowledge of right and wrong, good and evil "on their hearts." So obtaining it from the fruit was redundant. And tormenting them merely an act of capricious abuse.
Furthermore, they were (supposedly) the first people ever in the world. Nobody had any experience with anything. How would they even comprehend "lest ye die" as consequences, when nobody had ever died, ever? And didn't even happen (i.e. was a lie). Without the knowledge of right and wrong, good and evil, how would they know that paying attention to this heart-writing was the right thing to do?
The mental gymnastics to try and salvage this stupid fable about their omnipresent, omnipotent, omniscient god's omni-incompetence are Olympic-grade.
Spoiler alert: the bible makes no sense. And we're only up to page three.
Quite true. The only reason for them to have obeyed God was fear of punishment, which works even when the target has no conception that anything is right or wrong. Since one of the main purposes of religion is controlling people by fear, this serves the purpose well enough, but needs to be glossed over a bit to keep the "moral" veneer intact.
They were set up to fail.