I'm just worried about what effect this outing will have on the book's skyrocketing popularity with hardline Christian groups stateside...
Probably none.
Seriously, the only people who pay any serious attention to the extreme religious right over here are they themselves, and candidates during election years as they try to rape any votes they can by any means available.
Well, and the occasional nut living in a compound in Montana or Arkansas or something, but we pay even less attention to them than the religious right.
Frankly, I could care less whether the old guy is straight, gay, or likes to get his freak on with goats. It makes absolutely no difference to the story, which is why I must agree that really, Rowling should just STFU and write the books. Character details that have no direct impact to the story you're telling should be left to the audience to flesh out. It goes back to that whole "imagination" thing that, y'know, those things called books have made use of for centuries in order to bring the audience in, and make them feel closer to the characters by building their own ties and conclusions.
If you want to make your book political, or it's somehow pertinent to the story at hand to make one of the secondary characters gay, then have the gonads to put it in your book to begin with. If you don't, be quiet, I'm reading.
Back to the idea of what impact this may or may not have on the popularity of the books themselves, again, I say very little. If anything, it will probably be more positive (overall) than anything else, since controversy always draws a crowd. Sure, there's probably already some idiot somewhere burning their kid's book collection, but for every one of them there's probably at least 10 others going, "Really? Wow. I gotta check this out and see what all the fuss is about."
Americans love a show, and for most of them, it doesn't even matter if the show is actually any good. If it gives them something to point and laugh at, or some means by which to step out of their own sad little lives for five minutes and focus on someone else and their problems, it's all gravy. In the end though, we're basically a nation of rubber-neckers. We see a car crash on the interstate, we just *have* to stop and have a look, no matter how horrific it might be. Dollars to doughnuts gets you, this won't really be much different. Some people will scream bloody murder about "the corruption of children and traditional family values", others will scream just as loudly about the "fair and equal representation of the gay community in mainstream media", and most people will just shrug and go, "Eh, good book. Someone pass the salt."
-Wraith