Exodus 20
4 "You shall not make for yourself an idol in the form of anything in heaven above or on the earth beneath or in the waters below. 5 You shall not bow down to them or worship them; for I, the LORD your God, am a jealous God, punishing the children for the sin of the fathers to the third and fourth generation of those who hate me, 6 but showing love to a thousand {generations} of those who love me and keep my commandments.
7 "You shall not misuse the name of the LORD your God, for the LORD will not hold anyone guiltless who misuses his name.
Harry Potter is wrong because Deut. 18:10. Saying "God" at the beginning of the sentence of a daily conversation or when you are annoyed or angry at someone (for example when people say "Oh my God") is wrong. Singing hyms while an image of an artist's rendition of Jesus is being displayed up front is also wrong. Telling children's stories while showing them a picture of a human's idea of Jesus is also wrong...
Yet we select the things that for us are absolutely wrong and will speak against, we select the things that could be up for personal interpretation, and we select the things that are obsolete and useless in our times. We would all make very good lawyers, bending and twisting words and ideas to justify ourselves. I think God foresaw that and inspired Paul to write the following:
Romans 14
1Accept him whose faith is weak, without passing judgment on disputable matters. 2One man's faith allows him to eat everything, but another man, whose faith is weak, eats only vegetables. 3The man who eats everything must not look down on him who does not, and the man who does not eat everything must not condemn the man who does, for God has accepted him. 4Who are you to judge someone else's servant? To his own master he stands or falls. And he will stand, for the Lord is able to make him stand.
5One man considers one day more sacred than another; another man considers every day alike. Each one should be fully convinced in his own mind.
(The underlining is my own)
It's important to share ideas, but to share them like an ultimatum, to say that Christians do this but they dont do that is wrong, in my personal opinion. I think we can share our ideas, say why we believe that, and accept the other person's point of view, never condeming anyone. So to say Christians dont watch Harry Potter would go against the biblical principle of not judging anyone.