I don?t know what you?re talking about when you say Ms. Rowling?s response to the fan was inappropriate and thoughtless. Arguably, what the fan said was inappropriate and thoughtless (and maybe even a little bit homophobic); she didn?t give a reason as to why she ?can?t see Dumbledore that way?. Did she expect him to burst out of the ground in a rainbow tutu singing It?s Raining Men or something? Or that we needed an entire chapter devoted to Dumbledore making out with Grindelwald under the moonlight, because it was much more important than destroying all the Horcruxes and killing Voldemort like the fans actually wanted?
Rowling said her character?s gay, so her character?s gay. A fan asked a simple question, and she got a simple answer. Why does an author need to have a reason to make a character gay when they don?t if their character is straight? Would we be having the same discussion if she wrote a fanfic in which Spider-Man was a Sikh living in London?
There?s nothing wrong with analysing a creative work, or arguing (as some may?ve) that it was a rather trite political statement since she announced it after the series had already ended (although, if it was political, she could?ve chosen any character to be gay) and ol? Albus was the only character explicitly noted to be homosexual in a baker?s dozen of various characters for which sexuality was never even made a topic (and why should it be? It?s a book series about a bunch of teenage wizards and witches trying to defeat Magic Hitler).
I mean, a long while ago, the manga author Toriyama seemed to have decided that Tenshinhan (Tien) from Dragon Ball was a descendant of a three-eyed alien clan, giving an explanation as to why he had a third eye in the first place and could do stuff like grow arms out of his back and duplicate his body. Many fans disagreed with the statement, saying that there never needed to be an ?explanation? for all the oddities that Tenshinhan ? or, for that matter, a whole host of weird characters in DB (e.g. Kuririn?s lack of nose, whatever the fuck Chaozu was meant to be) ? had, and that it lost the fantasy element of his character. But it was designed to be canon, so? it is.
What about JoJo?s Bizarre Adventure, another manga series? The source material itself, as well as one of the supplemental materials that came out after the subject in question, stated that the Stand, ?The World?, is DIO?s Stand. But some interpret various events and inconsistencies in the story itself to in fact be telling us that ?The World? is the Stand of Jonathan Joestar and DIO just stole it. And depending on who you talk to, what happens towards the end of Part 7 supports or contradicts this. (It?s set in a different universe anyway, and the author, Araki, still hasn?t come out and said whether or not it?s the same universe as the one created in Part 6).
Or how about the question of whether or not Rick Deckard is an android in Blade Runner? Ridley Scott, the director, said he is; Harrison Ford, the actor who portrayed him, said he isn?t. (Not to mention, that film?s been released, like, three times now, each with various omissions and additions that can change the mood of an entire scene.) Who?s right and who?s wrong? Does anyone have to be right or wrong? Should we just go by the book it was loosely based on, where Deckard was in fact a human? Whatever, just go with your own interpretation without trying to make everyone agree with you.
You don?t have to think of the character that way, but you can?t change authorial intent. Why should she have to justify her creative decisions if she doesn?t want to or thinks the request is stupid?