Christ personally gave the disciples the power to cast out demons. Paul cast out the spirit of divination in the slave girl that followed them around in Phillipi. But others with no authority, like the Seven son of Sceva, discovered the hard way that messing with demons is no game when done outside the power and authority of God.
As for Bob Larson I may have to return to this discussion later about him, but I have one of his books on spiritual warfare and I believe that he truely does encounter real demons and has cast them out, but the big question is whether all the cases are legitimate. I've also heard some complaints about his ministry in some other financial scandals, but that is unrelated to the reality of the spiritual interactions he has in exorcism.
But yes, Christ came to destroy the works of the Devil, and Satan and his fellow fallen angels are not idle, but rather active amongst mankind today. In the power of the Spirit God can rightfully enable Christians to cast out Satan & demons and bind the Strongman by Christ's power. But it must be exercised with discernment and not as foolishly looking for a fight like the Seven sons of Sceva. We don't need to go picking a fight but neither should we fear Satan or be passive to his advances, for greater is He who is in us than he who is in the world.
That is a very short and rough summary of my take on the issue. Feel free to probe me for elaborations.