It kind of goes along with “Why does God allow bad things to happen to good people?”
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If God allows free will then free will is granted to both good and evil people. God didn’t “cause” the Holocaust, but by his just nature of granting free will he had to let it happen.
God returned to us the “Tree of Life” in Jesus
He also allows us still to eat from the tree of good and evil, it’s our choice
God chose to give us his power to do his work on earth.
The most terrible things that happen here are because the good allow the evil to stand unchecked.
Why did the church allow Hitler to get that far? Hell, some of the church helped him.
In many cases, we are the blame for the atrocities on earth, not God
Your point of “without evil we would not know what is good” is right. This is a perfect example of the metaphor of the tree of good and evil. Man did not know evil until their eyes were open in Eden. We were not created to judge good and evil, we only knew good until then.
If God allows free will then free will is granted to both good and evil people.
Not to be too hard on the questioner but asking that question serves no useful purpose. Nor do the questions I posed.
To do so only wastes what precious little time we have on this earth to make it a better place.
We make it a better place by making "good" decisions. Thanks to Adam and Eve, we now have that power.