Really, it's inevitable given how popular the books are. The "Shipping Wars" (mostly between shippers of Ron/Hermione and Harry/Hermione) are only one example of what the fans can't agree on. Excluding these and the aforementioned Base Breaking Characters, we can cite the following issues:
- The seventh book's famous/infamous epilogue. The Babies Ever After ending is sometimes felt to be too sickly-sweet and even lazy, whereas others think it's a hopeful look at the future.
- Are snakes sapient? The fact that you can talk to them through Parseltongue suggests it, but others think the idea is simply too strange and prefer to think the magic of Parseltongue itself temporarily heightens the creatures' intelligence.
- Similarly, the Dementors' true nature is a divisive topic, though one of the "softer" cases inasmuch as it rarely causes full-blown Flame Wars. Are they undead, or a species of their own? And provided they are, are they just another sentient species that happens to be saddled with "dark" powers, or pure evil, or even not truly sentient at all?
- The true nature of Dark Magic is a long-standing subject of argument in the fandom. Is it truly a different type of magic that is intrinsically different, or simply a semantic denomination for any "harmful" magic that may otherwise be from other branches of magic? If the former is true, then could it be that Dark Is Not Evil and some of the Dark spells could be used for good?
- On a related topic, the protagonists' absolute taboo against killing their opponents on purpose in the canon books is looked down upon by some fanfiction writers who think it is a naive, childish outlook on the world, and that the war couldn't realistically be wrong if the heroes didn't actually try to mow down the ranks of the enemy rather than simply defending themselves and capturing them whenever possible. Others share Rowling's morals and think becoming cold-blooded murderers, even in a state of war, would mean the heroes were going evil themselves, but many feel that said message flies in the face of what The Real Heroes undergo in the face of reality, and the entire message and intended concept is more or less inapplicable and unrelateable.
- The whole Fanon concept of "magical cores". Are there inherent magical power levels in canon, or is it just a matter of skill, so that anyone could achieve Dumbledore or Voldemort's level if they worked hard enough?
- Was Hermione's S.P.E.W. an ill-conceived, but conceptually right attempt at freeing long-abused slaves, which only goes wrong because the Elves, having been born slaves, tragically don't want the freedom they deserve? Or is it an instance of Hermione trying to force her own Muggle values on a different world, and failing to understand that while they shouldn't be mistreated, it is House-Elves' nature to be obedient servants? A third faction sees it as a tone-deaf Fantasy Conflict Counterpart that makes a utter mockery of Slave Liberation in history and contemporary society, whose payoff in the books is unsatisfying, detrimental to the character arc of one of the most favoured supporting characters (Sirius), and which works by violation of Show, Don't Tell and use of Informed Wrongness and Values Dissonance.
- Was Voldemort a born psychopath, who was not right in the head from the start? Or did he only turn evil because of his horrific upbringing? Word of God supports the latter, but that doesn't stop fans from speculating.
- Rowling's universe expansion with the introduction of the American magic school Ilvermorny and history of magic and wizard society in the USA was met with this, particularly from American fans. Some liked the new additions to the overall universe and the new materials to work with while others were heavily critical of how poorly researched the material felt with regards to American history (especially Native American history, the Salem Witch Trials, and America's own complex racial relations), culture, and politics. At best, it feels superficial and lacking any nuance; at worst, it's offensively insensitive and stereotypical. There was also a meta-backdraft from fans over accusations of Rowling being racist, as racism is something she got famous for speaking out against.
- Another point of contention is how well the series as a whole has held up since it concluded in 2007. It is still well-regarded in many respects (such as the worldbuilding, likable characters, and its meta-legacy within fandom culture and on Young Adult literature), but over the years since the books concluded, a growing backlash began brewing among adult fans who've revisited the series and more people became increasingly critical of it, pointing out various plot holes, characterization issues, and other narrative inconsistencies that have bogged it down. Other complaints that fans had even during the books' run, such as Harry's abusive childhood with the Dursleys being Played for Laughs and Snape's wildly unprofessional behaviour as a teacher not being disciplined even after several students complained about it multiple times to the other Hogwarts staff, have only become louder as well due to changing cultural values further condemning abusive behaviours. Rowling's tweets (both Word of God supplementary materials and her own real-life political views) definitely haven't helped either.
- Were the Slytherins really mostly bad guys due to being brainwashed by their family traditions, or did they look like that because the series is told from Harry's point of view and as a Gryffindor he mainly interacted with Malfoy, Snape, and Voldemort, all of whom he highly disliked/ hated? The debate is far from over.
- The only actually valid reason for Harry's return to his ridiculously unfit guardians every summer was because of the blood-protection charm that Lily's Heroic Sacrifice had created that protected him from Voldemort and the Death Eaters as long as he was underaged and living with a blood relative. Dumbledore also points out a couple times that it was rather useful in stopping Harry from becoming full of himself due to being exposed to fame at a too early age. Whether this was ultimately worth the abuse Harry got instead is constantly debated.
- Whether Rowling was right to go through with her last-minute decision of killing off Lupin and Tonks instead of Arthur Weasley is something which some people still debate.
