I don’t think we can say that God truly sent the devil — also known as Lucifer, or later as Satan — down to earth in quite the way your question envisions. While the devil was cast out of God’s direct presence in heaven, this did not happen because God actively wanted Satan to have sway over his creatures.
Question Corner: Why did God send Lucifer down to earth?
Father Ron Rolheiser: On not locking our doors
“In all the great religions of the world, in the end, being with others is heaven; ending up eternally alone is hell.”
Pope: God does not lead us into temptation, Satan does
The Italian and English translations of the “Our Father” can give believers the wrong impression that God can and does lead people into temptation, Pope Francis said.
Late exorcist’s words lift the veil on the demonic, Satan
By Allan F. Wright “An Exorcist Explains the Demonic: The Antics of Satan and His Army of Fallen Angels” by Father Gabriele Amorth with Stefano Stimamiglio. […]