I suspect there are two reasons why this is not far and away the single most contraversial topic in the entire series. Firstly, that we are, as a culture, aclimatized by books like Oliver Twist (and many of Dickens’ other works), Huckleberry Finn, The Little Match Girl, Jane Eyre, A Series of Unfortunate Events, and many many others all feature characters that suffer abuse. It is not uncommon at all that a child protagonist has to deal with situations that should not exist. Secondly, because many (most?) of the authors commenting on the series are not actually analysing its moral message, but rather debating what constitutes a satisfying story.
Mrs. Rowling, in writing the series, has chosen a writing style that, if is not in fact an example of an unreliable narrator, certainly comes very close to it. Nearly everything is told from Harry’s point of view, with extensive use of the third peson limited writing style and only minimal shifts to other perspectives. Thus, with few execptions, we know only what Harry knows, and, more importantly for this conversation, we view as remarkable only what he views as noteworthy.
Thus staying out of Vernon’s reach barely deserves a comment1, and we barely blink when Petunia’s frying pan comes close enough that Harry feels the need to duck.2 The Dursleys are abusive; for a variety of reasons Mrs. Rowling has simply chosen to understate that.
The easy answer for this abuse is that the story demands it: I have observed that it is next to impossible to have child protagonists in conjuction with responsible adults. The Dursley’s casual abuse gives Mrs. Rowling much greater flexibility to put Harry in situations that a responsible guardian ought to be objecting to. Stepping back from that easy answer however, what is the in world logic for this? Why are there no other responsible adults who step in to intervene, or even attempt and fail to intervene, in Harry’s life?
In giving us the obscurial, Mrs. Rowling has created an answer to this question. The idea of abusing a child is deaply frightening to most of the magical world. The costs of doing so are so high, so potentially life threatening for the abusers (and, unfortunately, for the child as well), that it is nearly unthinkable. Thus society has no mechanisms to deal with the problem.
On a side note, This is one aspect of the descriptions of MACUSA that rings true, the so called ‘pure-bloods’ in charge of the British Ministry of Magic would not hesitate at a solution to mundane-on-magical abuse that consisted of kidnapping the child and giving him or her to a magical family. So even families that are not aware of [obscurials] do not pose a true obstacle to this in-world logic.
Not only does society have no mechanism to deal with it, the fear would combine with cultural influences valuing the family lineage (whether that is based on socioeconomic class or magical ability either one) to create an atmosphere where child abuse is virtually unthinkable not just unhandled. You might neglect a child to the care of house elves (as the magical equivalent of nannies); you might be emotionally abusive to a child you think has no magic (and thus no risk of being an obscurial), but you simply do not physically mistreat a child.
The obvious exception to this is Walburga, who from all accounts had no problems with cursing her own child. However, remember that Sirius left for Hogwarts the first time certainly healthy, probably reasonably happy, fairly typically spoiled rich brat. We have no evidence that she became violent towards him before his sorting. After his sorting, now in possession of his own wand and undergoing magical training, it is reasonable to guess that he is no longer at risk of becoming an obscurial. Even if that is not true, unknown in world, or up for debate either way, it is equally possible that the woman is simply insane, and an exception even for her own society.3
Mrs. J. K. Rowling. Harry Potter and the Half-Blood Prince American Kindle edition approx Location 611 of 8473.↩︎
Mrs. J. K. Rowling. Harry Potter and the Chamber of Secrets American Kindle edition approx Location 148 of 4470.↩︎
PepperonyOwl There is no escape Published: 2022-08-17. Updated: 2023-03-04. Chapter 5: The fallout↩︎