The writer Robertson Davies was plagued from childhood with waking dreams and nightmares of a witch chasing him, trying to catch and eat him. He would wake up, paralyzed with fear. These dreams followed him into his adult years, until finally in one dream he turned to the witch and asked her, "Can't we be friends?" The witch became a kindly figure and took his hand, ceasing to be terrifying.
How can a witch mean? Davies took this to mean he had gained some mastery over his fears; a Freudian might say he'd finally come to terms with complex feelings about his mother; a Jungian that he'd reconciled himself with a fearsome aspect of his own personality. All three might be talking about the same thing, from a different point of view. The witch is a potent symbol, and a complicated one.
A distinguishing characteristic of the witch, be she good or bad, is a full out, straight ahead, all-or-nothing attitude. Most human beings amble along in life, neither very good nor very bad; a witch goes over the top in search of knowledge or power or simply in a rage of life. The extremes of her personality (often characterized as hunger) take her into an amoral, inhuman zone. Even a good witch, like Granny Weatherwax, can terrify by her strict code. It is the enthusiasm, the verve, the full depth of experience, that makes the witch an appealing character.
This could be why lots of people would like to be a witch (a storybook witch, with nothing to do with the dreary Satanic or neo-Pagan witches). It's not simply the magic powers; it's living beyond the work-a-day world and common definitions of behavior that appeals. In this sense witches are rather like pirates as epitomized in recent movies: they steer by their own compasses and can be as moral or immoral as they choose. Witches have been metaphors (in literature) for the artistic, the bohemian, the outsider who sees a part of life that ordinary society denies. Who hasn't felt an admiration for toads and owls and crooked trees that most people would brand ugly or useless? Who hasn't felt the impulse to go after one's desires as single-mindedly and without thought of cost as the Wicked Witch of the West goes after the Ruby Slippers? It's the pointy hat showing itself, and for good or ill we're usually forced to push it back down.
As a metaphor, and not only as folklore or history, the witch will always be a potent symbol. The witch is like the world, or like life itself: the sooner we come to terms with them and put them in their proper place the better off we are.