If Adam and Eve do not know the difference between good and evil, then they cannot make rationalisations based on morality. To them, killing a dog for sport and raising it as a pet are morally equivalent (a fitting analogy as they were vegetarian).
Therefore, the only thing that could inform their reasoning was their base knowledge. They did not eat from the tree because God told them it would kill them. The snake told them it would not kill them, but would instead make them like God. Adam and Eve are aware that God is better than them, and want to become better, and so eat the fruit, having been informed that it will not kill them.
This action to them is merely a rational decision, and yet God punishes them for committing an immoral act they could not possible have known was immoral before they committed it.
God wanted blind obedience - if he did not, he would have informed them of all the facts: "Do not eat from that tree, it will give you the knowledge of good and evil, and I don't want that, it'll make you miserable. If you eat it, I'll have to punish you". Instead, he told them it would kill them.
Blind obedience is, in essence, a ban on rational thought. If you are told to obey, instead of to think and offer input, instead of deciding on your own, the thinking is being taken out of your own hands, and put into the hands of someone else. Rational thought is forbidden.
Furthermore, if you take the stance "God knew that they would want to eat the fruit when they heard what it was, so he didn't tell them what it was and just that it would kill them", then this further serves to hinder the "the objective wasn't to ban rational thought" narrative. He knew that the rational outlook would have been to eat the fruit, therefore he withheld knowledge, and left them to make the 'rational choices' based on incomplete information.
There is no version of this story in which Adam and Eve have actually done anything morally wrong. They disobeyed an instruction, which (let's accept this as given for a moment, though it's not true) is morally wrong, but they couldn't possibly know until they'd done it. They just ate yet another fruit, like all the other fruits, which they now knew wouldn't kill them. How is any of it their fault?
