The cultural left is against her for being very visibly transphobic (along other things). Additionally religious reactionaries historically don't like the fact her books are inspired by historical witchcraft practices, as pointed out in the meme.

To quote wikipedia's summery:

...Whited asserted in 2024 that Rowling's sometimes "flippant" and "simplistic understanding of gender identity" had permanently changed her "relationship not only with fans, readers, and scholars ... but also with her works themselves".

https://en.wikipedia.org/wiki/Political_views_of_J._K._Rowling#Transgender_issues

Ok. Since you have clearly been living under a rock for the past 10 years, here's the deal with Rowling. It's not really a political divide here, it's an age divide.

Harry Potter was a formative experience for almost all of Millenials and Gen Z. That's 40 years worth of kids right there. A lot if Gen X parents were fans as well. There's a lot of gay/trans people who credit Harry Potter for helping them figure out their identity and come out to their friends and family. And Rowling is a master of cultivating a fandom; ask anyone between the ages of 40 and 12 what their house was, and I'm pretty sure you'll get an answer. My point is, there are a lot of people (people who are adults now) who have formed their identity around Harry Potter, and Rowling made sure that it was seen as normal to get so invested in her books.

Problem is, Rowling is a Blairite Conservative, and you can see this all over her writing. As kids, we didn't pick up on details like how the plot bends over backwards to not have any change happen in the world, how few girls there and how all the bad ones are ugly, the house elf slaves, etc. So when Rowling started to be more loudly TERF-y, we collectively went through a few phases of realization about how wrong we were about her:

1. Wait, how could someone this conservative have written the books I remember?
2. Maybe we can just pretend that she didn't write the books? We can separate the art from the artist, right? Maybe I can just buy all my merch secondhand?
3. Oh god her books have bad politics all the way through them, you can't even pretend that these weren't written by a conservative!
4. Am I bad for liking these books?
5. You know what, maybe I am done with Harry Potter.

To address another thing that might confuse you, I know that I've been using TERF and conservative somewhat interchangeably. To define my terms, when I say "conservative" I mean Rowling thinks the world was perfect at some point when she was a young adult and any attempt to change how the world works from that point is Evil and Bad. The Trans Exclusionary Radical Feminist movement was seen as progressive in the 80s and 90s but has remained almost exactly as it was back then, so now it only contains "moderate" conservatives. To be fair, her political beliefs are pretty in line with most members of the Democratic party in the U.S., so I understand if you thought she was left-wing. But she is very clearly a conservative, and more importantly her whole fanbase was at minimum progressive liberals and many are much farther left because, you know, millenials and gen z have on average only been moving further left as they get older. Another thing exaggerating this is a fun little statistic that 67% of all book readers are girls, and guess which subset of Gen Z is most likely to be anticapitalist?

If she had just stayed quiet about hating trans people, I think Harry Potter might have been remembered as one of the most world-changing works of fiction, at least up until Gen Alpha gets old enough to enter academia. But she just had to use her platform to try to spread her beliefs, and now she's so hated by her own fandom that attaching her name to a project is sure to make that project never sell, and any actually successful Potter-related project has to constantly reassure potential fans that they do not hate trans people, they are not associated with Rowling, Rowling has no involvement in their project, and a portion of our profits will be donated to a nonprofit that helps Trans kids. For example, Hogwarts Legacy did all of these things, and despite its good sales and despite most fans enjoying it there was an abstract dread looming over the project as if the fans expected Rowling to interfere with their enjoyment at any moment. It honestly just makes me sad that there are so many adults that feel so wounded and betrayed by their favorite author.

The way I reacted to this was to stop joining fandoms altogether, and I still feel icky when something I like has a fanbase. I don't think this is healthy. Maybe I will work through this someday.

She's a huge bigot...

I don't think you can categorise into right or left. I know right-wing people who are gay as an example (they're conservative, but they're not MAGA/Trump/nazi's).

It's really better to categorise as "people who want the community to be better and want everyone to be treated well", and "people who want people to receive different treatment".

JK Rowling is the latter. Trump is the latter too. In general though, in US and Australia, extreme right wing people seem to fit more into the latter.. Minorities can also fit into either category too quite easily

nobody on the left would ever say that someone who does one cool thing is automatically a good person. There's been plenty of asshole artists and overall thing makers in history that have made amazing things