When people are trying to decide right from wrong, many people attempt to make a list of things to "do" and things "not to do". This is usually in the form of don't drink, don't smoke, don't watch R rated movies, don't dance, don't etc....
Often these lists of "do's" and "don'ts" address issues which are not directly addressed in the Bible. People do want to know the bottom line, can I play Dungeons and Dragons or not. In reality, the list becomes an additional law besides the moral law, the 10 Commandments. We need to be careful about adding to the list. On the other hand there are a lot of things that have moral implications which are not addressed in the 10 Commandments. While I believe in one sense they are addressed, in another sense things like illegal drugs, pornography, movies, gothe clothing and a whole list of other topics are not addressed in their modern form. The underlying issues are not new but the forms are.
Role On Brother
The core to a role playing game is that it is a game that involves the imagination. Some people enjoy that but others don't. Role playing takes a lot of forms besides those in a game. For instance, there are plays, skits, opera on the artistic side of the house. But on the more practical side, astronauts, pilots and soldiers go through simulations and exercises which are in their essence people playing roles. Firemen, ambulance drives and policemen also go through similar training. We even do this when we have a fire drill. Sometimes we play roles to have fun; sometimes to practice for life situations. Playing roles is a human activity that few people could really say is sin.
One thing about role playing, a person can act in a way that he does not normally get to do. This is the point of a fire drill. However, in the world of fantasy, many people like to change their persona through costume or role playing in order to do things they would not normally be allowed to do. While not everyone who goes to a night club is in this category, some people who would normally dress and act quite conservatively, once they dress the part, they act outrageous once properly in the role. In other words, playing the role helps them loose some inhibitions. If loss of inhibitions helps someone overcome a fear, that is an healthy thing. My creative drama teacher told the story of how as a teacher she helped an extremely shy little girl. The girl would not say a word to anyone. The teacher used an orange sheet as a prop for her class. The teacher gave the sheet to each child and asked what they imagined they were. One girl wadded it up and held it like a baby, she was a mommy. A boy draped it over his shoulder, he was a Roman soldier. When the extremely shy girl's turn came the teacher threw the sheet in the air. The teacher let it fall on the girl and she said, “I’m a pumpkin". The world of make believe helped her to participate in the group. But loosing inhibitions is not always healthy, especially if the inhibition keeps one from sinning. It is not unusual to used role playing as a way to engage in illicit sexual behaviors. Violent angry feelings are played out in certain games. Another area that people would not normally avoid but when playing a role allow themselves to dabble in is the occult.
9 When you enter the land the LORD your God is giving you, do not learn to imitate the detestable ways of the nations there. 10 Let no one be found among you who sacrifices his son or daughter in  the fire, who practices divination or sorcery, interprets omens, engages in witchcraft, 11 or casts spells, or who is a medium or spiritist or who consults the dead. 12 Anyone who does these things is detestable to the LORD , and because of these detestable practices the LORD your God will drive out those nations before you. 13 You must be blameless before the LORD your God.
My own exposure to Dungeon's and Dragons is when my good friend in high school got involved. He was smart and a good Christian. His playing the roles made him comfortable with going to a fortune teller after his SAT. (He wanted the fortune teller to tell him what he made.) While I'm not saying that everyone who plays D and D will do such a thing, dabbling in the occult is more acceptable once the it is done repeatedly in a game. And I want to again say that I do not know how much the occult is a part of D and D anymore. It might be a very different game than it was in the late 70's/early 80's.
It would hardly be possible to remove all role playing from our lives, nor would it be desirable. When we do play roles, it is okay to do so to have fun and for training purposes. However, we should not allow ourselves to let role playing be an excuse to sin.