if JKR was in favour of trans rights you'd suddenly think she was overrated and full of herself.
You're dead wrong there.
I still like and respect Margaret Atwood, and read her books, despite her saying TWAW.
Some of us can bear people having differing opinions - even if I would ask her some searching questions if I ever got the chance. 
I also haven't denigrated Emma Watson in any way at all (others here may have - that's their call - but I bet no feminist has told her to "suck their dick" because feminists don't tend to do that...) because I actually quite like her. I've seen Emma Watson get horrific online abuse from men, when she spoke at the UN, and awful sexualised attention from men and trolls - upskirting/objectification/talking about when she'll "legal" 
It was disappointing to see her in the queue to stab JK in the back. It just makes me despair of some young women a bit - in such a hurry to give away women's rights in favour of trans rights.