If Adam and Eve had no knowledge of the concepts of good and evil, they had no way to know that disobeying God and eating the forbidden fruit was actually wrong. They didn't obtain that knowledge until after their transgression. So, was it actually fair for them to be punished?
They were told not to eat from the tree. They ate from the tree. Was it unfair that they had to face the consequences of eating from the tree?
On another note, God did not immediately dismiss them, as he very well could have. He waited. He called to them, and waited until they finally came out from hiding (don't forget that they did hide from God when he called, that's important). When God asked what they had done, what did Adam say? It was the woman you gave me, that caused me so disobey you. And when God asked Eve, what did she say? It was the serpent. The snake talked her into it, and to giving the fruit to Adam.
What does that sound like? Did either of them say," yes, I did eat the fruit, even though you told me not to. It was through my own fault, and no one else's." No, they didn't. They blamed something else. Don't punish me, God, because I didn't really do it. Even though you gave me free will, and that you told me not eat of the tree...it wasn't really my fault. Honest.
They knew they had a choice. They also had a choice in telling God the truth. It's not about disobeying God, or being punished by God. Adam and Eve punished themselves. They hid from their acts, then lied about them.
But honestly, isn't that what we all do? We try to avoid facing mistakes as long as possible, until finally it hits us right in the face.
I think in the end, Adam and Eve realized their mistake...or more likely their mistake hit them right in the face. Once that happened, they realized they had pushed themselves away from God. God did not abandon them, they abandoned God.
So is it fair? No, it's not. Is it permanent? Of course not. We are making the same mistake that Adam and Eve did even today. We can still fix that.
It's a little long, but I think it answers your question.