In 1972, Bill Finger, uncredited co-creator of Batman and Robin, gave an interview that remained lost until 2008 and unpublished until 2011; in that interview, to my great surprise, Bill was asked about the sexual orientation issue. Here is his response:
What about his claim that Batman and Robin were homosexual fantasies?
I knew many homosexuals but I certainly didn’t think of Batman in those terms. I thought of it in terms of … Frank Merriwell and Dick Merriwell, his half-brother, who was the kid he was taking care of. … In America we always talk about the Western hero and the pioneer kind of man—the Davy Crockett types—as being loners. They’re never really. They always have a sidekick. … Certainly there’s no homosexual relationship. It’s just part of the American syndrome. … It was just that the author realized that you’ve gotta have somebody to talk to. Sherlock Holmes had Watson—were they homosexuals? Baloney. You just can’t have your hero walking around thinking aloud all the time. He’d be ready for the men in white coats after a time. So we created a junior Watson and that’s all [Robin] was.
Incidentally, Bill's only son Fred (who died in 1992) was gay.