Thinking "I could never be a bigot" is the first prerequisite for becoming a bigot.
In the UK we've seen a few people ride this crazy train to the end of the line in the last few years. Perhaps because our political landscape is different from that of the US, it's easier to see it happening. There has never been an expectation here that being a conservative means you will hold insane views. It might mean you have some objectionable political ideologies, but you are still expected to be a somewhat normal human being who occupies the same planet as the rest of us.
So when we see somebody make the transition from being just a bit right-wing in their thinking, to being a full-on conspiracy lunatic, it really shows. We've seen it with a lot of our politicians and other public figures.
There's a guy called Neil Oliver who used to present historical TV. His views were always a bit weird and biased (historians and archaeologists did not like him at all), but he wasn't an actual crazy person. But he rode that crazy train to the end of the line and became a fully-fledged antivaxx COVID denier, who is now babbling about one world government and peddling antisemitic conspiracy theories. It happens.
JK Rowling's radicalisation has really disturbed people, because she was famous for books which championed ideas of equality and rights for marginalised groups. In retrospect, those books had some biases and prejudices in them as well, but they were ones that most white Britons carry without realising it. So the seemingly sudden change from that to being someone spreading hatred of trans people and seeming to consciously back antisemitic ideas was a massive whiplash. A real shock. Even more of a shock than the fact she seems to have forgotten how to write a readable book.
Now, I'm a pro-independence Scot who was active on Twitter in the years after 2014. So I already knew she was disingenuous, a bit of a troll, and had some fairly reactionary views. Perhaps her further radicalisation was less of a shock for me. But it still took me aback.
This happens. It happens to people who are too secure in their own self-concept as a Good And Progressive Person. They feel that because they are a Good And Progressive Person, all their thoughts and feelings and biases must also be Good And Progressive, because Good People don't have Bad Thoughts, and of course, Bad People never have Good Thoughts.
By painting JK Rowling as having always been a secretly Bad Person, and Harry Potter as having always been secretly propaganda for Bad Thoughts, we make ourselves vulnerable to the same kind of radicalisation. The truth is that she is just a person, a white cis woman with some unexamined biases, who wrote a series of books that were good-hearted and had good messages, and also reflected some of those biases. And now she has taken a ride on the crazy train, and it's scary to see.
Because it could happen to any of us.