Scripture tells us not to delight in those who do evil. Is it wrong to watch and enjoy a movie that displays sorcery like Harry Potter?
The sorcery condemned as a work of the flesh (Gal. 5:19-21) comes from the Greek term pharmakeia, from whence we get our term “pharmacy.” In biblical times it primarily was defined as the use or the administering of drugs and poisons. It was also used in connection to sorcery that was connected to pagan idolatry (cf. Is. 47:9; Ex. 7:11, 22; 8:18; Rev. 18:23). Historically, the worship of pagan idols included drugging and poisoning people in order to either sacrifice them or induce hallucinations which would then be attributed to the magical powers of the pagan gods.
Not having read or watched the Harry Potter books or films, but having seen the trailers and read the reviews of them, I gather that the Harry Potter books and films have fictional characters within them who use magic for good or evil purposes. I’ve also observed from viewing similar films like Lord of the Rings that the magic done within them is quite different from the pagan idolatrous use of drugs which was the definition of sorcery in biblical times. The sin of sorcery in the Bible had nothing to do with waving magic wands or magic walking sticks in order to truly and literally cause doors to open out of thin air and people to levitate, as is done in modern fiction like Harry Potter, Lord of the Rings, and various comic book movies. I likewise do not see these films as promoting pagan idolatry as something positive and worthy of participation, as sorcery did in biblical times. Thus, I see no biblical reason to indict watching and enjoying these films and books as inherently sinful.
Pre-Denominational Christianity 
Well, sorcery is also defined in the OT as things like omen-reading (presumably for money, as God sends real omens like the star of Jesus to save lives, and people shouldn’t make money off of grace like that even if their insights are correct), trying to contact or raise the dead, talking to spirits, Moses’ enemies transforming staffs to snakes, etc.. So it’s not just drug abuse.
That said, I think you’re right to say Harry Potter is fine. I personally believe that all fiction is fine- for one thing, God warns us repeatedly about everything that’s dangerous, and fiction is never mentioned as being on that list. For another, Jesus likened the Pharisees to children confused as to why He isn’t going along with their make-believe games. We’re clearly supposed to draw a line between fiction and reality, but He never condemns fiction itself. In fact, God commissioned artists to place statues of birds in His Temple, and had the invention of music remembered forever– with no attached criticism or warnings- in the early part of His holy book.
So no, fiction isn’t bad (as far as I know), nor is it supposed to mimic reality. It would be impossible for any mortal artist to do that. (And the magic in Harry Potter is a natural gift, nothing related to demon worship, anyway.)