I think its important to keep in mind that Rowling is not depicting true Witchcraft - anymore than Tolkien is when he refers to the Lord of the Nazgul as the 'Witch-King'. Both have constructed an entirely negative pseudo-'witchcraft' - for Rowling it has 'positive' connotations, for Tolkien negative ones, but neither of them are attempting to depict Witchcraft as it actually is. I had a long correspondence some years back with an initiated Witch & he was as friendly, compassionate & decent a guy as you could wish to meet (or hear from
).
The point is, Witches draw their 'power' from a 'Higher' (or perhaps it would be better to say a 'Deeper') source - whether that source is seen as 'nature' or the Goddess, or the God & Goddess. Satanism is a Christian heresy & clearly did not exist before the appearance of Christianity.
Now, the point of this is to try & make sense of why (some) Christians seek to ban the HP books. They are
not trying to ban Witchcraft, because they have no real idea what Witchcraft actually is - they confuse/conflate it (often deliberately) with Satanism, & are seeking to 'ban' that. Basically, what drives them is a desire for control.
Unfortunately, Rowling has fed into this 'Christian' power trip by misusing the terms 'Witch' & 'Wizard'. While she has presented her Witches & Wizards in a positive light, she is not actually presenting true Witches at all. As a result she has given her child readers a totally fallacious concept of Witches. Her greatest 'sin' in this regard has been in not placing her 'magic-users' within a philosophical/religious tradition. For instance, true Witches would go out of their way to avoid doing harm, as they believe that any harm done to another -
particularly harm done by magical means - will cause the Witch her/himself to suffer three times the harm in return.
So, the problem with Rowling's approach to magic is that it lacks this philosophical/spiritual background - true Witchcraft is a highly complex spiritual path which requires years of dedicated work & study to master - years in which those who only seek power & self aggrandisement will tend to drop out or learn better.
All this is a very roundabout way of saying that what Rowling is presenting in her books is neither Witchcraft nor Wizardry, & certainly not 'Satanism' - which is a horse of a very different colour. Looked at in this light, what certain 'Christian' groups are doing is less attempting to ban a fantasy but rather
using a fantasy as a weapon to ban another religious tradition. Unfortunately, Rowling has aided them in this by deliberately refusing to give a spiritual tradition to support her Witches' & Wizards' practices. She has also, because of this, offered a very misleading idea of what Witchcraft actually is - principally, that it is both easy & self serving. From this point of view it is difficult to argue that her books may do harm - not to the children who read them, but to the followers of other spiritual traditions - Witches & Pagans in particular.
Having said that, most Witches & Pagans I've come across like the HP books - for the way Witches are presented in a positive light at least. Mind you, they have suffered from some very negative 'Christian' propaganda over the centuries.