Sci fi still lags behind in LGBT diversity. When Sci fi does bring diversity, more often than not it's a hot lesbian. Hot lesbians are great, but it's frustrating not to see gay men and trans people.
Warehouse 13's Steve Jinks is gay. He hasn't been shown in a relationship, though, aside from one episode where he was reunited with his ex-boyfriend.
I think we're getting a larger number of LGB characters in SF lately. They've been a fairly frequent presence in
Doctor Who -- most notably Captain Jack and Madame Vastra & Jenny, but multiple others as well. And practically everyone in
Torchwood was at least a little bit bi. We've had a lesbian regular in
Stargate Universe, and the current
Dracula limited series portrays Lucy Westenra as a closeted lesbian. Of course
Lost Girl has plenty of "hot lesbian"/bisexual action, but we've also seen at least one gay male couple in a guest role on that show. Oh, and Felix Dawkins on
Orphan Black is flamboyantly gay and promiscuous, something the show has portrayed fairly graphically.
Orphan Black also features a lesbian couple, Cosima and Delphine -- although Delphine is technically bi, because Cosima is her first female lover.
For the larger part of the audience this isn't a pressing issue.
Racial inclusion wasn't a pressing issue to the larger part of the audience in the '60s and '70s either. The majority can't learn to broaden their horizons until someone has the courage to challenge their prejudices. And that's a role that the media have often played in the past, and that
Star Trek was noted for playing, including people of color in its vision of the future even though doing so might not have been a "pressing issue" for "the larger part of the audience."
To what advantage does having a gay character bring?
Same as the advantage of any other character. The key is to get over thinking of them as "gay characters," as if that's their entire identity, and understand that they're just people like everyone else, that they have relationships like anyone else, and that it doesn't fundamentally make any difference whether the people they have relationships with are of the opposite sex or not.
Plus, of course, there's the obvious fact that a lot of people in the audience are LGBT themselves and would be more inclined to watch if they didn't feel excluded and marginalized. The broader the audience you appeal to, the bigger your audience can potentially get. Advertisers realized this about African-Americans 50 years ago: they watched TV, they spent money, so it was just good sense to include people they could identify with in TV shows so they'd be more motivated to watch, allowing more products to be advertised to them. It's just good business sense to be inclusive.
It's not something too many writers or creators or producers are going to take a chance on for anxiety over alienating some part of their core target audience.
Fortunately that's an outdated concern. The generation that's come to adulthood in recent years considers sexual orientation far less of an issue than their parents did. We can see this in election results, in the increasing number of legislatures legalizing gay marriage. And there's a lot more LGBT inclusion on TV today than there was a decade ago. Oddly it seems to be less common in genre shows than in mainstream shows, but they're catching up, I think. After all, most TV shows are aimed at younger viewers because they're the most active consumers. The prejudices of the older generation would therefore have progressively less sway over TV programming as time goes on, just as they have less sway over social legislation.
Since it hasn't happened yet in popular visual sci-fi then it possibly speaks to creator/producers not yet ready to tackle it.
Once again: Jack Harkness, Steve Jinks, Felix Dawkins. Okay, I feel W13 has been too timid about it, keeping Steve fairly asexual beyond often talking about being gay, but that's progressive in its own way because it treats him as just a person who happens to be gay rather than defining him by that one trait.
Orphan Black, meanwhile, has been anything but timid in its portrayal of Felix. And
Torchwood was pretty overt in its portrayal of guy-on-guy couplings, especially in the US-produced
Miracle Day.
I know there was a bi female in Babylon 5 (Commander Susan Ivanova) and I love Babylon 5 as a series. And Ivanova was a major character. But admittedly a bi or lesbian female isn't usually seen as threatening to a male audience and Ivanova was done rather lowkey when it came to her sexuality. It wasn't something they really dwelled on.
B5 was embarrassingly timid in its attempt to be "progressive" with Ivanova and Talia. They kept it all off-camera and implicit so that you were barely aware of it at all. Whereas its contemporary DS9 was pushing the envelope with "Rejoined" and the passionate, lengthy, on-camera kiss between Terry Farrell and Susanna Thompson. That stirred up a nice bit of controversy and helped push the envelope in the portrayal of lesbian relationships on TV. But we've come so much further today. Yes, there's still a way to go with the portrayal of male same-sex relationships, but showing women making out on TV is no longer even a big deal.
Not being gay I'm at odds at seeing this as a pressing issue because I don't personally feel unrepresented in science fiction.
I'm not gay either, but I am human, and that means I feel diminished when any other human being is excluded or belittled just for having some difference from the majority. Why should empathy be limited only to those who are exactly like oneself?