When I was a kid there was at least one gay super hero in the books I read. It's nothing new. The only issue is what Zosiasmom pointed out about canon. Don't go around messing with established characters. If you want to do some weird alternate universe stuff or make a new character that is fine. Just don't have batman come out of the closet and have a crush on Robin. Although...
Yeah anyone who is "threatened" by this weak attempt is hypersensitive. If I was gay I would be pretty pissed. This isn't even worth mentioning. Frankly the gay marriage in the Xmen title wasn't worth mentioning. Northstar has been gay since I was a kid. Nothing new there. It just showed how hypersensitive the far right is.
I collected comics from the early 80s until the mid-90s. I mostly collected alternative titles because they had more grown-up themes. Comics *can* be progressive, but the mainstream titles especially tend to operate on a "don't rock the boat" basis, IMO. I don't see how it can be a "slap in the face", but it certainly seems like DC overhyped the change. But then, that's marketing.
A lot of my gay friends were actually excited that it could be a series title the way it was implied and then...nothing.
Northstar was gay and in the Xmen in the 90s. I think building it up and then doing something week like that is a slap in the face. Either do it or don't do it. But don't jerk people around and use them a marketing tool... especially with that issue.