Before I begin, I would like it to be clear that my choice to join the 'Yes' side has nothing to do with my support of the announcement and everything to do with the fact that I believe readers have little to no right to decide what authors can or cannot disclose about their own fictitious characters. I do not pretend to understand the exact intentions with which the announcement was made, but when all is said and done, JK Rowling is the one who created the character, so she gets to decide all things concerning him. It's foolish to find fault with the author for making such information public.
While reading some of the articles written in the 'No' side of the argument, it became apparent that there are actually some people out there who feel they know what the Harry Potter series is about better than the author does. Though I hate to call into question the intelligence of my fellow writers, this form of arrogance borders on idiocy. I can't tell whether this stems from an unjustified feeling of offense at either the fact or the lack of discretion surrounding it, or a blatant attempt to feign some form of competent literary analysis. Either way, it only serves to waste both their time and effort critiquing something that have no say over. The only advice I can give to such individuals is this: Don't bother whining about things that can't be changed. If it really bothers you, read a different book. I'm sorry if it sounds rude, but my opinion stands.
One of the biggest arguments against this disclosure is the "fact" that Harry Potter is a children's series. I'd like to point out that, though it certainly started as a children's series, it grew up as the characters did, moving from a children's series to a young adult series. I certainly hope the young adults of our society are not so immature as to be unable to handle having a homosexual character in any of the books they read. Also, in today's world, with people being more open about such things, it seems foolish that so many people are in an uproar about it. In truth, the adults writing these arguments seem far more injured by this announcement than any of the children who have read these books.
Another point I'd like to make is that, while writing starts off as a craft, it ends as a business. The Harry Potter series has taken JK Rowling's business into the film industry, the publishing industry, the video game industry, and the manufacturing industry in the form of toys, decorations, etc. All of these require publicity in whatever form possible. While her announcement caught people off guard and bothered many, it also got their attention. People remember it. Remembering a product is almost always good for business. Was this the original reason for disclosing the information? I couldn't say for sure, but it worked.
The bottom line is this: for whatever purpose, JK Rowling chose to clarify that aspect of Dumbledore's character. That was her decision, and she's entitled to it - even if some readers are close-minded enough to be put off by it.