The snake is in the garden of eden, right? The snakes temptation was accepted "to know." ..... Basically to know evil. To feel it, be tempted by it, experience the pain of it, experience the cheap thrills of it, experience the addiction of it, experience the double-edged sword of it.

So the devil told the truth, they would have their minds opened to an entirely different realm.

Cipher in the matrix says: "Ignorance is bliss, while he eats the steak"

What if the true answer is this: "Innocence is bliss"

The devil ruined innocence. Was he lying about the increase of knowledge? Not really. Would we have been better off without this knowledge?

You decide.