I think you'd find the same people defending JK Rowling would likely be calling out people doing the same for Britney, seeing as much of the Britney hatred is misogyny.
James Corden has mostly alienated his fans because he went to the USA. I don't know but I believe that will be most of the negative feedback he gets. Or people saying he's not funny. As a comedian, that's a fair point. I don't see people randomly staffing that they dislike him for a feeling on the internet, and I would assume that the Corden fans would, quite rightly, call them out on it.
If you genuinely, genuinely think a woman who survived domestic abuse, is a self made millionaire, a feminist, inspires most of the subjective hatred of her based on, what, the fact that she sports a layered cut? Has a grating voice? Then I can't help you because to me it's blindingly obvious.
It's certainly not comparable to hating a man like Tom Cruise, whom there have been numerous documentaries on his borderline abusive/cult led values.
Thing is you're expecting jk Rowling fans to be held to a higher moral code than everyone else. If Beliebers are ok to argue that you can't dislike his music unless you've listened to his albums, then why can't feminists ask what baseless dislike is coming from and pre emptying it by directing them to her essay.
And besides, I doubt anyone saying that they dislike Rowling on a baseless feeling are given anywhere near the level of abuse or death threats she receives. So sorry, my sympathies are limited.