This response is coming from a guy who played D&D for over 14 years. Here are the good points of the game. It taught me about fantasy in which I am now a writer of, it turned me on to authors such as C.S. Lewis and Tolkien (both Christians), it kept me close with friends and helped me stay away from other influences that I could get into, i.e. drinking and drugs.
Bad points of the game. I basically forgot who God was during the time I played. I never read His word, nor spent quality time with Him. Basically all my life was praying to God before I went to bed. I wonder sometimes how many times my prayers actually went through lol. This game, like anything in life took up too much of my time and my focus strayed away from God.
During the time I played, me, nor any of my other friends tried to cast spells. We were all Christians playing the game for the most part. We never held any organized meetings to kill people, we never played the game on drugs, we never thought about taking the game higher than what it was. It was a game to us an nothing more. Sure we had sword fights with each other, but what kids don't get out with friends and play like your a knight?
But as time went on I began to get personally convicted about the game. Not because I thought it was evil, but because it enveloped so much time. If the devil can't make you bad, he'll make you busy. Anything to take your focus off God and that's what the game did. It's all about moderation. The game can be fun when it's played sporadically and not religiously. As for teaching people about witchcraft, I never saw that take place. We always knew our boundaries.
If you are personally convicted about the game I would recommend quitting. Its obvious the Holy Spirit is dealing with you about something. Remember if something is not of God, it is of the devil. Also in the book of Thessalonians it says stay away from all appearances of evil. So if D&D looks evil in your eyes, stay away from it.
This is my two cents for what it matters. So I guess I'm neutral about whether Christians should play the game. I'm a Christian and it never affected my life other than taking away my time. Pray about it and see what God tells you.