What makes JKR's shitshow even harder to process is that she didn't just ruin a book series. Harry Potter was an entire subculture. Like Star Wars and Star Trek fans, Harry Potter fans dedicated their lives and careers to the series. I don't know if I'd call it "underground," but liking Harry Potter got you beaten up when I was in school, so it was more of a dedicated indie culture than a mass-appeal fanbase.
Harry Potter was so huge that fan works developed their own followings. Potter Puppet Pals racked up hundreds of thousands of followers and was nearly as relevant as the series itself. For fanfiction, Harry Potter and the Methods of Rationality got so big that it has a Wikipedia page. The band Harry and the Potters spawned the wizard rock music genre. A Very Potter Musical developed a fanbase and launched Darren Criss's career.
Harry Potter also has extensive ties to fandom history. Everyone in my generation (millennials) remembers coming home from school to read Harry Potter fanfiction on the Internet. Today, most people just post their stories on Wattpad or Archive of Our Own. But at the time, the fanbase was splintered between fanfiction.net and dozens of individual websites and forums, some made for specific ships. Since they all had individual hosts, a lot of those sites have been lost to time.
And there's the infamous My Immortal fanfiction, which is an Internet legend with people still searching for the author. Everybody read that one (and laughed at it) in middle school.
Pre-social media, fan sites like The Leaky Cauldron and Mugglenet had massive followings because they were one of few sources for news, theories, essays and fan content. Some of these sites still exist after being around for over a decade and building their own legacy.
Before Deathly Hallows came out, fans were so desperate to know what happened that Mugglenet published a book called What Will Happen in Harry Potter 7: Who Lives, Who Dies, Who Falls in Love and How Will the Adventure Finally End? Yep...Harry Potter was so big that people wrote separate books about what would happen in an upcoming book.
And that's not mentioning all the book release parties, Harry Potter-themed events, monuments, fan films, restaurants and even a theme park. A lot of fandoms have those, but Harry Potter infiltrated every aspect of popular culture.
Today, there's a thriving culture of "Harry Potter adults" with themed weddings, baby showers and Etsy stores. Putting your Hogwarts house in your Instagram bio is pretty much a prerequisite for joining the "bookish" community. Warner still produces new content, like the Fantastic Beasts series, although we've all seen what a disaster that's been.
Everyone has at least a few memories associated with Harry Potter even if it's just watching the movies. I had great memories associated with Harry Potter. But looking back at the subculture, history and thousands of fan works, it doesn't seem fun anymore. Studying the fandom or being part of it comes with an awkward tension because you don't want to seem like you're condoning JKR's bigotry but can't divorce her from the series. This subculture was spawned by a woman who turned her legacy of magic and wonder into one of abuse and hatred.
I don't expect people to write paragraphs about how much they hate JKR every time they post about Harry Potter, but it's still uncomfortable to see people make new content or wear their Harry Potter Etsy tote bags like nothing happened. Even if they clarify that they don't support her, it's just a weird, tense situation for everybody.
People dedicated years of their lives to running Harry Potter fan sites, writing fanfiction, cosplaying characters and making fan movies. If I were in that situation, I'd have a mild identity crisis. I'd ask myself "Did I waste all those years? Should I delete my content? Where do I go from here?"
So ultimately, JKR didn't ruin "just" a book series or even "just" a fandom. She tanked an entire culture, which inspired people to look at Harry Potter more critically. The issues that people brought to the light tainted the series's legacy even without JKR's personal issues.
Once, Harry Potter was a series for generations. Now, former fans hope that the series fades into irrelevancy. Unfortunately, JKR didn't just tarnish her legacy--she took decades of history, millions of fans and a worldwide subculture along with her.