I think people fear what they do not understand. Each person has the right to choose what they allow their children to watch.
I see that Harry Potter shows that Good can overcome evil, and that friends and family are the most important relationships etc.
I believe that you can find "evil" in anything if you look hard enough. Same with the "Good". I think Harry Potter is what you make of it. I personally think it is a great story. As the books evolve, the characters are older and so is the audience. So I would reccommend reading/watching it first and go with your gut. Even be prepared to discuss some of the aspects of the book with your child, highlighting the lessons you want them to learn.
Just a side note: the Catholic Church does not approve of Harry Potter but does approve of the Chronicles of Narnia. They are the same genre. It is just what you choose to see in it.
Just my thoughts. I am not judging anyone for their opinon. I think you just have to follow your heart and let Spirit be your guide.
N.
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