It's possible that they just don't understand the appeal of fanfic in general. They might see it as a waste of time or a less - than - worthy form of writing. And when it comes to Harry Potter fanfic specifically, they just lump it all together and say'screw them' because they don't see any value in it.
One reason could be that they are a huge fan of the original books and movies and think that fanfic often takes things in the wrong direction. They might feel that the creativity in fanfic goes against what they love about the original Harry Potter, so they reject it completely with that statement.
Perhaps they've come across some fanfic that contained offensive or inappropriate content related to the Harry Potter world. This could have turned them off so much that they have a negative view of all Harry Potter fanfic and express it in such a strong way.
Maybe they just don't understand the real essence of Harry Potter. They might have only seen a small part of it or misinterpreted some of the more emotional or character - developing moments as signs of weakness, which is completely wrong.
Someone might say it if the fanfic contains really bad writing. Like if the grammar and spelling are atrocious, it can be a turn - off. Also, if the story is just plain boring or the characters are not well - developed.
Maybe it's a way of stating that the integrity of the original Harry Potter character is not influenced by fanfic. Since fanfic can sometimes deviate greatly from the original source, saying 'harry potter doesn't care fanfic' is like saying the original character remains untouched by these fan - created ideas. Fanfic often has different interpretations of characters, and this statement could be a way to uphold the original view of Harry Potter.
Well, 'screw them' is a rather unkind or dismissive phrase. In the context of 'Harry Potter fanfic', it might imply that the person has a negative attitude towards Harry Potter fan fiction, perhaps they don't like the way some fanfic writers handle the story, characters, or they just generally don't like the whole concept of fan - created stories within the Harry Potter universe.
Perhaps they haven't fully understood the series. Some people might just skim through the books or movies and miss out on the depth. They could be focusing on just the surface elements like the magic spells and not realizing the complex relationships and themes beneath.
Perhaps they've come across some really strange fan - created stories. Some fanfictions can be very out there with their interpretations of the wizarding world.
Perhaps they don't fully understand the depth of the world - building. They might see all the magic and think it's just some random, crazy ideas thrown together like in a not - so - well - thought - out fanfic.
Maybe they just want to be controversial. Some people like to make extreme and untrue statements to get attention.
One reason could be that they feel the official Harry Potter story has a defined end, and the fighting in fanfiction is just over - done. They want to focus on the original tale's conclusion.
Maybe they want to emphasize the purity of the original 'Harry Potter' story. They don't want it to be confused with the many fan - made stories out there.