When I was a kid I loved Heinlein, Asimov, Piers Anthony, Howard, Lovecraft, among dozens of other then popular scifi and fantasy authors
Heinlein is some weirdo libertarian fascist
Asimov hates women and was a notorious sex creep
Zanthony is a pedophile and his books are full of creepy shit
Howard was staggeringly racist
Lovecraft is also famously racist.
And that's just the ones off the top of my head.
At some point I learned that all these guys were creeps, came to terms with it, and moved on with my life. Like an adult.
So all these people whining that "oh no I can't let go of my childhood!!!!" fill me with contempt. Many of the great shit-head scifi/fantasy writers of the 20th century made great contributions to the field of fantasy and sci fi. Our conception of robots wouldn't be the same without Asimov. Heinlein changed military sci-fi forever. Howard's Conan had a lasting impact on fantasy fiction far beyond what was merited by his mediocre writing. Lovecraft introduced the notion of Cosmic Horror that continues to push back the borders of science fiction today.
Rowling can claim none of that. Her wizard books are extremely mediocre with poor plots, flat characters, and no new ideas. Their popularity is the result of a then unprecedented marketing campaign, not any particular artistic merit. They're entirely pedestrian and forgettable and there's no reason to read them except as a historical curiosity or a case study in successful marketing of children's literature.
I gave up many genuinely influential and talented writers when I realized that they were jackasses. There was nothing riding on it. No one is using Lovecraft to justify violence against Inuit people or something. I just found out they were jerks and said "Well shit. Guess I won't recommend these to kids anymore".
And all these jackasses have the audacity to say that we should respect their love of the mid wizard book beause it's so important to them?
I still recommend some of Lovecraft's work, and Asimov's, and other shitty people's. But always with warnings, with the intent to discuss their flaws and the way those flaws creep into their work (or, sometimes, take over the work wholly) and the way that those works can still be valuable and cool and worth looking at despite those flaws in author and work.
The problem with Harry Potter is it doesn't really have any redeeming qualities. It is, as you say, worth nothing more than good marketing. I wouldn't recommend them to anyone mostly just because they're not very good, even with Rowling completely out of consideration.
If they were good? I don't know, it'd be a different story.
With Lovecraft particularly, i'd argue that at least for me, his works were worth reading because they are so infected with his perverse ideas that it just derails and jumps from disgustingly racist into plain ridiculous. I mean, come on, the guy is literally afraid of trees and soap bubbles and star constellations. He lives in a constant state of dread and disgust, and that's what all reactionaries are like deep inside. Lovecraft lays bare the soft, vulnerable underbelly of the reaction. Cosmic horror is the inability to handle the world as it is, without mythological, purpose-simulating blinders on your eyes, the utter failure to see the beauty in life's sprawling chaos, the common L of the Appolonian. Lovecraft shows us the reactionary mind at its most miserable, when these people cannot pretend to be the violent, muscular Herrenmenschen they dream themselves to be, but when we see them for what they actually are: terrified little men who have to roll for sanity loss when they see me walking down the street and can't decrypt my gender.
I'm not saying this because i want to recommend the guy, i'd particularly advise anybody who's been racialized against getting too deep into this shitshow. Being able to do a close reading of reactionary material without distress is always privilege, i know from personal experience how much of a difference it makes when all that hate and terror is aimed at people like yourself. I can't even begin to describe the damage transphobic narratives in mainstream media did to me, and i'm dead certain that for a lot of black & brown comrades, the same applies to the demonization of racialized and indigenous communities in works like Lovecraft's. But for the time being, this material is out there, it has shaped how our culture conceptualizes certain tropes, and when you know it already and can stomach to bring it up again, it's absolutely worth reflecting on and understanding the thought process and especially the emotional state behind it, because it's a good way of knowing your enemy.
I should also add that i never gained the same insight from JKR's work as i did from HPL's. Looking at her writing with the knowledge of its not-that-hidden-bigottries didn't teach me anything new, i just saw into the mind of somebody who is incredibly plain and petty and has never had an original thought in their entire life.
Strong agree with that last bit. Lovecraft remains useful because he's smart and insightful and creative in the way he conveys his bigotry and terror and prejudices on to the page. Rowling isn't smart enough or reflective enough to do any of that. You can learn something from Lovecraft that can be applied to understanding how bigots think about the world, but Rowling never really had anything to say.