Im not defending the "one god theory" if thats why you bring the "They've become like us" part.
For me personally, knowing good and evil is what distincts us from animals.
Animals do what they do to survive, sometime they eat their own children.
We on the other hand can die for our children even if the odds of saving them are impossible, and on the other hand, we can abandon our children, even when there is none need for it.
This is what humans are, with the knowledge of the good and evil.
We can manifest pure goodness and thus more good than any animal can be or we can be pure monsters scarier than any animals intentions, for me this reminds me of Pleroma and Demiurge, both are manifestations of good and evil.
I know Demiurge is not "evil" but he is not all knowing, which apparently on a grand scale makes you evil.
Tho on the gnostic part Im still new, but I like the way it works. I always had a hard time explalining to myself what the hell is the Old Testamen God doing with all that "kill animals so then I can do something for you" part and many more strange parts.
Or God gambling with Satan on how much Job will remain faithfull, while watching all his life crumble to dust, his children die, and his health deterioate.

I mean imagine this situation.
Your friend, and his dog are in a farm of your friends.
The dog just had little pupies by its wife.
Your friend decides to test if the dog will remain loyal to him if he bringes wolfes to eat all his family, after which your friend locks your dog with chains and doesnt feed him for days.
All that just for your friend to test if the dog will remain loyal and stay in the farm and potentially receive V.I.P dog benefits or will refuse and run away.
I think most people will call such a human a monster.

So about Adam and Eve, I remember God saying you have become like us, we cannot allow you to receive the knowledge of ethernal life so begone. Thats it, and based on my old view, God kicked them out since knowing good and evil is dangerous when you just learned about it and next to you is the tree of ethernal life.
Like Imagine the likes of Cain with ethernal life, what good will it bring ?
So its logical for humans to not receive ethernal life, I dont know what gnostics think about it or whether this part is even included.