When our Lord entered creation via incarnation, a primary thing He did was take on evil and demonic powers that had entered His good creation.  He did not come to declare that evil was somehow good, meant to serve God’s greater purpose.  He knew evil was evil with no good in it.  He defined it in order to defeat it.  His casting out demons must be seen as the warfare He came to wage.  In the end the powers of darkness will be cast into the lake of fire, and God’s good creation will blossom without the decay of sin, death and demonic influence.  Jesus’ disciples have come to take back territory that rightfully belongs to their King.

“So the great dragon was cast out, that serpent of old, called the Devil and Satan, who deceives the whole world; he was cast to the earth, and his angels were cast out with him…The devil, who deceived them, was cast into the lake of fire and brimstone where the beast and the false prophet are. And they will be tormented day and night forever and ever.” Revelation 12:9; 20:10 (NKJV)