Over at The Corner, which is a group weblog for the Conservative National Review, a reader is quoted as making what the editor there calls a good point…
How can a fictional character be anything but "openly" gay? When they describe Barney Frank as the first openly gay congressman, they mean that there may have been others, but they kept it to themselves. Fictional characters don't have lives outside of what their audiences can see. We, the audience, know everything they do and everything they think (via those little bubbles). It's only a comic book for crying out loud!
The easy answer, I suppose, is that the character can be "non-openly" gay in the continuity of his or her stories. The readers, may know he or she is gay via "those little bubbles" — we in the know call them thought balloons — but the other characters don't. So the character is "openly" gay in the sense that the plots deal overtly with that.
But a more useful answer is that, as company-owned characters get handed about from writer to writer, each of us creates our own version of the hero — one that we usually hope does not conflict with the ongoing continuity. (I say "usually" because some writers consciously wish to leave their stamp on a classic character, which can be a good idea if they have good ideas and are there for a while; a bad idea when the writer is especially transient or just trying to grab attention.)
And in doing our versions, we project some aspects of ourselves and/or our acquaintances into the character and supply our own subtexts and motivations which may not be evident. Certainly, when I've written Superman or some other iconic character, I have thoughts about him that never make it onto the printed page. It's the same way an actor, called upon to display a certain emotion, may reference a personal memory in order to evoke that emotion. You have to weep over your dead mother but since your real mother is still alive and sitting out in the third row, you privately think about that goldfish that died when you were eight. In the same way, writers are always secretly drawing upon experiences and personal feelings, or basing some facet of a character on themselves or a friend or relative.
There have been comic book writers — openly gay or closeted — who have written classic characters over the years. Just as gay songwriters write about loving "her" when they really mean "him," some comic book scribes have probably penned scenes of Superman loving Lois Lane when they really meant Jimmy Olsen. They don't put it overtly into the script because they know it won't be accepted…but it's there and, once in a while, some readers pick up on it. And it isn't just gay writers who can impose a gay subtext. It wouldn't surprise me at all if some heterosexual writers had written Batman and decided to base their Robin on a homosexual they knew. We've certainly seen a lot of cardboard, unconvincing lesbian tendencies imposed on female characters in lieu of more realistic characterizations.
The critic above is right that fictional characters don't have lives outside of what's on the paper. But we don't always know everything they do and think. At least with the more ambitious writers, there's always that which is implied between the word balloons. And it could just be that the villain would rather kiss the hero than kill him…and is attempting the latter because he can't do the former.