One religious answer to the problem of evil is the idea that sin is necessary in order to allow people to exercise their free will. Apparently, if God had created a perfect world, we would all be robots with no free will, and that would be a terrible thing.
But wait a minute. Heaven is supposed to be a perfect world. God, the angels, and all the saints are supposed to live in heaven forever. If free will requires sin in order to be free will, then the sinlessness of heaven means God, the angels, and all the saints are going to spend eternity not having any free will.
That means that for us to have free will right now is a complete waste. The only thing it contributes is to send most of God’s “beloved” children to the eternal torments of Hell. Only the elect few will make it to the realm where their free will no longer exists, and the Bible says that the saved were foreordained before the foundation of the world, so in a sense their “free” will was illusory even while they had it. That’s not much of a justification for sin, is it?