I think it must be said that witchcraft being forbidden is not just a Catholic Church teaching, or a Roman obsession against witches. It is from the Bible:
Deuteronomy - chapter 18:
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 their 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; because of these same detestable practices the Lord your God will drive out those nations before you. 13 You must be blameless before the Lord your God.
So Pagan witches I understand but… Christian witches? Just because they are baptized people practicing witchcraft does not mean they are Christian witches. It is the same as one identifying themselves as Christian + other sin. Who says for example - “I am a Christian liar”?

As long as they realize that their practices are Pagan (and most of them I think they do, online I have met only witches who consider themselves Pagan, they are not interested in Christianity to say the least) they are realistic.
Many of them are atheist in the sense that they worship more like elements and certain old figures mostly women, they respect the planet and are interested in ecology and such. They have no respect for demons either and are sure that demons are just a type of energy misunderstood by Jews and Christians. And usually they think “the Bible is just one book there are many others.”
But when we discuss “Christian witches” we talk about something else. We talk about a Christian who may be using Divine energies they get from communion or Holy devotional objects in ways God made it clear in the Bible He does not approve of. We have to explain to them that they are wrong if they define themselves as Christians, they have an obligation to know any better.
Plus the way out of it is not that hard. Correct me if I’m wrong, but the Church considers witchcraft a sin. and like any sin it can confessed and there are canons to be followed to achieve forgiveness.