I'm not sure how clearly this has been addressed in this thread, but . . . .
Sexuality and romance =/= gender.
There is nothing wrong with including sexuality and romance in your D&D games, as these things exist in the real world they also exist in whatever fantasy world you play your games in. But if your group wants to downplay sexuality and romance and focus on other human activities, like violence, that's fine of course
But you can't eliminate gender in your games (well, unless you are playing in a really weird fantasy world). You can blissfully ignore that not all humans fit neatly into the gender binary, in the modern day as well as the ancient past (and everything inbetween), and likely in any remotely "realistic" fantasy world (realistic as in the "suspension of disbelief" -- look it up). But you are missing out on something important if you do.
If you are a heterosexual person, and you were playing in a game where all of the characters, PC and NPC, were homosexual (even without any focus on sexuality and romance), that *might* feel a little unwelcoming and jarring to you.
If you are homosexual or transgender, playing a game where it's been acknowledged that your character can be of whatever gender orientation you want, and that certain background characters (NPCs) have varying gender orientations, is very respectful, welcoming, and can make you feel more "safe" participating in that game.
If you, being homo or trans, enter a game where you're told, "We don't discuss "sex" and so we don't want to hear about your homosexual or transgender character", well, then you are NOT being welcomed and something that is core to your personal identity is being dismissed by the other players. You'll be less likely to stick around in an environment like that.
Do ALL homosexual, transgender, or LGBT-friendly folks feel the "need" for this inclusiveness? Of course not, we are all individuals and we all respond to the inequities of society differently. Homo and trans folks have had to learn how to "get along" all their lives in a heteronormative environment, and we all have different priorities and comfort levels.
But I'll never understand the position of, "Well, despite many folks in this minority group telling me that this IS a problem, I've never seen it as such and so I'd just prefer we ignore it rather than deal with it and make something more welcoming to a greater diversity of people." But that is the liberal's conundrum, isn't it? How to be tolerant of the intolerant.