Long time geek, fangirl, mother, and reader. I've got a lot to say, you might not like it all, but it will be honest and hopefully helpful.
"The interesting thing about the Harry Potter fan community, and something that separates it from the majority of fan communities, is that they are not fans, per se, of J. K. Rowling, Warner Bros., Daniel Radcliffe, or of any other individual. They are fans of a book series, its related subjects."
An Excerpt from Percy Weasley’s University Thesis
by Chris Rankin
This is not a unique feature of the Harry Potter fandom. Most media series with intricate world building and high concepts inspire passion about the world, and philosophies.
Just ask the fans of Lord of the Rings, Star Trek and Star Wars. Tolkien's books not only inspired the creation of an entire new genre in high fantasy, not to mention studies of the languages and cultures in the books. Star Trek has similar explorations into the world and cultures in the series, much that was created by fans after the original series was cancelled. There is an actual Jedi religion, know as Jediism (Temple of the Jedi Order)
This is hardly a new phenomena.