What is a witch? Are we to accept the idea of an old crone with a broomstick and a black cat familiar? Or should we look at a follower of the modern practice of Wicca? What does the Bible mean by a witch?
There are various things addressed in Scripture that fall into this category. There is the practice of divination, attempting to determine the future by various means (Acts 16:16-19; Ezekiel 21:21-23), of casting spells (Acts 19:19; Isaiah 47:8-15), of performing wonders by one's own power (Exodus 7:11; Acts 8:9-11), or of being involved in communicating with the dead (1 Samuel 28:3-25; Isaiah 8:19). The underlying principle is the serious practice of magic (as opposed to the stage magician).
Scripturally, God is the only legitimate source of supernatural help. And He cannot be manipulated, only asked. From the Christian viewpoint the main issue is not good intentions versus bad intentions (white versus black magic), but taking to ourselves a power that belongs solely to God. Nor is the issue explicitly worshiping Satan. While I am sure Satan is flattered to be directly worshiped, in the final analysis he does not care who you worship so long as it is not God. While much of it is charlatanism, I do believe Satan and his minions can supply the supernatural power behind serious magic. (Acts 16:16-19 suggests this.) But this is not dependent on the practitioner's consciously following Satan. I know in my youth I dabbled in such things, and it at least seemed to work for me, though only on a small scale. But whether or not it works, it is wrong.
How, then, is the Christian respond to such things? First, we should avoid the use of all such things. I have known Christians to make excuses for such practices. It is also possible to approach spiritual gifts from an attitude of witchcraft, where we start to see them as our personal power rather then depending on God. But we can also become unnecessarily paranoid of witchcraft and everything associated with it. We need to remember that God is victorious over Satan and can protect us (1 John 4:4; Colossians 2:15). Therefore, we should avoid panicking at every mention of witchcraft or reading it in when it is not there. Witchcraft is wrong, but it is no more wrong than many other things our society takes for granted. We should not condone it, but we should face it boldly through faith in Christ.