I have a great idea, let's take a look at what Jesus told them to do when He sent out His 12 disciples, and then the 70 (which were not disciples!).
Matthew 10:7-8
7 And as ye go, preach, saying, The kingdom of heaven is at hand.
8 Heal the sick, cleanse the lepers, raise the dead, cast out devils: freely ye have received, freely give.../KJV
Luke 10:1, 17-20
1 After these things the Lord appointed other seventy also, and sent them two and two before his face into every city and place, whither he himself would come...
17 And the seventy returned again with joy, saying, Lord, even the devils are subject unto us through thy name.
18 And he said unto them, I beheld Satan as lightning fall from heaven.
19 Behold, I give unto you power to tread on serpents and scorpions, and over all the power of the enemy: and nothing shall by any means hurt you.
20 Notwithstanding in this rejoice not, that the spirits are subject unto you; but rather rejoice, because your names are written in heaven.../KJV
Mark 16:15-18
15 And he said unto them, Go ye into all the world, and preach the gospel to every creature.
16 He that believeth and is baptized shall be saved; but he that believeth not shall be damned.
17 And these signs shall follow them that believe; In my name shall they cast out devils; they shall speak with new tongues;
18 They shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall lay hands on the sick, and they shall recover.../KJV
Thats a fair account from 3 of the gospel books. Notice any similarities between them?
Every time as Jesus was sending them out He comissioned them what to do. (which was exactly what Jesus Himself had been doing!) He never sent them out without telling them to cast out devils I notice. Jesus did a Lot of casting evil spirits out of people! It's probably what He did the most!
Are you catching on yet? There seems to be a lot more people who are either possessed by evil spirits or at least are demoinized (Harrassed by evil spirits, enticed), so why do so few people cast out spirits nowadays? Or even talk about it?
Jesus taught them how to handle evil spirits. He gave us the authority over them in His name. He told us to do it. It wasnt just the Apostles, it was the 70 also which were normal people, Followers/Believers like you and I so we cant say it is not the duty of a Christian to do what the Lord said to do.
He made them learn about evil spirits before He sent them out to Evangelize.
What do you think? Is it our duty as good Christian Brothers & Sisters to cast out evil spirits? I believe it clearly is...