Satan sinned and then beguiled Eve and consequently Adam to sin. Did Eve rebut Satan, to say "no will not be as gods? Did she rebut Satan's accusation that God was hiding such a thing? No, she did neither. If you want to say she was naive because of her innocence, that I could agree with.
God knew before He created everything what would happen, and planned His means of salvation and redemption of man before the world was even created.
God in His great and passionate mercy made it possible for man to not reap the eternal consequences of sin because -
Jonh 3:
16 For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.
So we are saved because of God's great love. And it is by mercy and grace, not earned, nor deserving, that we are saved.
God's justice is a different facet of God, I think you may be confusing with love, mercy, grace - the basis of salvation.
----------------------------------------------------
God is just.
If Satan sinned and man sinned - would they not in justice both be equally condemned. Do them in Revelation 20, the great white throne judgment, who's names are not found in the book of life, cast into a different lake of fire, than Satan will be? No, because God is equally just.
Blessed are we, because God is also great in love and mercy. By which, He sent his only begotten Son to die on the cross for us, that we may be forgiven of our sins and receive eternal life.