I always think of, like, 2nd century scriptural debates when matters of canon come up.
General rabble: accepts bits from the movies and the books and maybe cursed child and that one fanfic they read when it crossed their dash. In general, whatever supports my ship is canon.
Proto-orthodox church fathers: The 7 books, 8 movies, Cursed Child, Pottermore, and everything from Fantastic Beasts including the new information in the trailer are all canon. If the books and the movies appear to contradict each other, your understanding is unclear. Maybe Harry walked into the forest twice.
Marcion: Fantastic Beasts isn’t canon. Cursed Child isn’t canon. The movies are not canon except where they provide a texturally harmonious expansion of the books. Pottermore and Twitter and interviews aren’t canon except where they support my main thesis. Those parts in the later books I don’t like are due to the nefarious influence of Steve Kloves. I will provide detailed textual arguments for my headcanons that contradict statements in material I consider noncanonical. I am a member of one or more character’s defense squads.
Plume de Lynx 