Cultures all over the world, for thousands of years, have recognized and accepted the fact that ‘gay’ people exist. Some cultures have even given them their own special positions within their societies.
It was not until very recently that anyone, anywhere, suggested that there was no reality (except in extremely rare, medically provable instances) to the clear biological sexual dichotomy of male/female. And that is what Rowling is arguing.
Point taken. But it has never been so much the argument that gay and straight are on equal terms, and that gays should be able to marry, and even worse, raise children, and they certainly should never have gotten the influence over society that they have now.