And what is this accusation based upon?
It wouldn't be the first time that Rowling's words on something have been taken out of context, so I really wanna know....
And besides, learn to see the art apart from the artist.... The quality of the books don't change, and Rowlings income won't change when you throw your books away... You already paid for them, so the cash is in, and there's nothing that can change that.
The famous composer Richard Wagner is said to be an antisemitist, even one of the people placing the ground of it on how it's expressed today (I've even heard that Hitler based his own ideas about Jews on Wagner's quotes about them), and yet, the Ritt der Walküren (in English known: as 'The ride of the Valkyries') is still played and praised, and even used in movies and computer games. (https://www.youtube.com/watch?v=rcZp7u_Krp8 <- I'm sure you've heard that piece before)...
It would be a shame if Rowling was indeed transphobic (can neither deny nor confirm that, I need to know on what this accusation is based first). And waving the gay flag in protest... Hmmm, there is a homosexual in the Harry Potter franchize, with a very important role too.... His name is Albus Dumbledore. And loads of people didn't take kind on that revelation either... Some people were actually shocked.... Oh well....