She’s one person influencing millions, if not billions, that’s for sure. She’s not some random author, she is one of the most well known personalities of the 20th and 21st century. Her opinions carry weight, as misguided as that may be on the part of her followers.
I’d partially agree with you if we were talking about some random who has sold a few hundred kindle copies of their book on Amazon and is spewing nonsense. And even then I’d call for people to not support that author in any way shape or form. JKR is however hugely influential, and that absolutely should matter when it comes to deciding who you give your money to.