When self-indulgence is at work the results are obvious: sexual vice, impurity, and sensuality, the worship of false gods and sorcery; antagonisms and rivalry, jealousy, bad temper and quarrels, disagreements, factions and malice, drunkenness, orgies and all such things. Galatians 5:19-21
Rebellion is a sin of sorcery, presumption a crime of idolatry! 'Since you have rejected Yahweh's word, he has rejected you as king.' 1 Sam 15:23
What I find interesting, and telling, about these passages is the Greek for words the English has variably translated as sorcery, divination, or witchcraft. In the examples above, St. Paul uses the word pharmakeia which can be translated as both sorcery and healing. Indeed, it is the root for the English words pharmacy and pharmaceutical. In 1 Samuel, the Greek is oionisma, which refers to a type of divination that interprets the flight of birds.
In other words, magic is like any other part of creation — its being good or evil entirely depends upon how it is used. Pharmakeia can be used to coerce or con somebody (sorcery) or it can be used to help people (healing). Oionisma was used by King Saul in a way that divorced it from God — he turned away from God and instead put his trust in the flight path of birds. The evil of magic is not inherent in magic itself, but rather in the way we allow it to turn us away from God.
It is fascinating that D&D instinctually portrays this dichotomy with its magic system — divine magic being granted by God in contrast with arcane magic which finds its source within the will of the user. It would be easy to declare all divine magic good and all arcane magic evil (which does put an intriguing spin on OD&D and B/X elves), but this ignores the history of the game and ignores my basic premise that good and evil of magic is determined by how it is used.
This doesn't mean, however, that both should be equally easy to use to do good. For example, a sword and an axe are both weapons designed to kill people; however, an axe is also a tool that can be used to create things. While it is possible to use both to do good, it is easier to use an axe for good than a sword. In this same way, I feel divine magic should be easier to do good with than arcane magic. This is inherent in that divine magic is more defensive and arcane magic is more offensive; however, I like my arcane magic a little more dangerous.
I have used a number of mechanics to accomplish this. I very much enjoy the Vancian magic interpretation of S&S, which requires a roll to successfully cast a spell, which may not take effect immediately even when successful. This does not, however, take into account the motivations behind the action — that which largely determines the goodness or vileness of an action. For example, healing someone so that they can continue to be tortured for more information is not a good act. In worlds where monsters are physical manifestations of sin, one can easily have fun with wandering monster tables when arcane magic is used carelessly. This is especially effective when you have tables with monsters based on the type of sins committed.
According to the Fathers of the Church, sin can be broken down into three basic categories: Irascible (wrath, despair), Concupisent (lust, greed) and Intellectual (vainglory, pride). Each of these categories can be countered with the traditional Christian practices of fasting (for irascible sins), alms-giving (for concupisent sins) and prayer (for intellectual sins). Using this background as a jumping off point, it is relatively easy to come up with some tables utilizing standard monsters:
5-6 Brain Lasher
It is also fun to design monsters that personify the various kinds of sins. Note that the character need not necessarily encounter the monster, or even be aware of its existence. Sin never just affects the person who sins, but also everyone around them. Thus, a character can bring a plague of monsters upon a neighboring community.
All of this makes arcane magic truly dangerous to use. Some side-effects of this reality that I like:
arcane magic users are going to be rare, distrusted and often Chaotic; magic is rare — the common man is too afraid to use anything associated with it; and elves are mysterious and dangerous — they aren't entirely trusted by other folk and they are as much a threat to those they help as they are to those they oppose.
Thus, it is possible to do good with arcane magic, its just not as easy as with divine magic.