One of the claims I see about why God doesn't just eradicate all evil this very second is that if God did do that, He'd have to wipe out all of humanity, as we all have evil tendencies.
But if God can only eliminate evil by destroying people, then how can anyone get to heaven? The whole premise behind the salvation and sanctification is that one is slowly changed to be like Jesus, and once one dies and gets to heaven, you are back to your original, pure, sinless state. And thus, no longer have an ounce of evil.
So if God is able to eradicate the evil in a person without destroying them, why can't He do the same to everyone? Or is this tied to He can only eradicate evil is someone has made the choice to repent and follow God?
To say that God can't destroy evil without destroying us comes across as saying that evil is an inherent part of our nature, something we were intended to have from the beginning. But the whole idea behind the Fall is that humanity was distorted from its original purpose -- and thus, evil isn't supposed to be an inherent part of anyone's character.