The point about thinking only bad people can be radicalised being dangerous is an extremely important one.
There was a time when JKR was viewed as the unproblematic queen of the left. It may not have been in the text but she made Dumbledore gay when it was barely legal to mention anything queer to children (I’m being very literal there. The first five books were published and the sixth written when Section 28 was still law and no publisher would have been legally able to mention a gay character in a children’s book).
At that time the very idea that she could ever be viewed as homophobic, or ever even remotely consider siding with a Conservative government on any issue was bizarre. The face she showed the public was inclusive and very anti Tory.
But she also went from as poor as you can be without being homeless to astronomically rich in a short period of time, had the eyes of the world on her and was really quite viciously stalked and harassed by the less ethical corners of the press. Her phone was tapped, her children stalked, friends she hadn’t spoken to in years and distant family members had people turn up on their doorsteps trying to dig up any possible story about her.
As a result she wound up extremely paranoid. I live in Edinburgh. A workman who came to fix something at my house told me he’d worked on a garden wall for her and there had been a rule of no phones allowed anywhere near her property and there was a line around the house that they weren’t allowed to cross or even approach. I’ve heard similar stories from people who have friends living near her.
People who live in that kind of state of paranoia (whether justified or not) are very easily radicalised by anyone who plays on their fears and offers any kind of safety, whether real or imagined. Yes, it could be that the bigot who has recently sided with the Tories on several occasions was always there underneath. But it also equally possible that in the past there was only ignorance on some things and that the bigotry and political swing is new and entirely the result of paranoia enabled radicalisation.
The desire to retroactively demonise everything she’s ever done and assume she was bigoted from birth is understandable, but it doesn’t reflect the reality of how people can and do change for a whole variety of reasons and that sometimes even the best people can become something you’d never have imagined possible.
It’s actively important to remember that good people can go down some horribly twisted paths, because if you reassure yourself that ‘good people’ will always remain good then you lose the ability to self reflect and examine your own ideas, or examine the difference between an actively malicious viewpoint and a confused and ignorant one.