Romance in Mass Effect can be... a little awkward. You just want to go have a chat with Kaidan about the ship, or to see how Liara's doing, and bam! Suddenly, you're in the middle of some forced and uncomfortable flirting.
It's more than a little awkward when you're playing the game with your spouse, and awkwardly flirting with the same girl he picked.
Even more awkward because in many ways, Shepard is designed to be an extension of the player's own being -- the customizable look and dialogue choices speak to this, and a very very large number of players make their first or canon Shepard in their own image. My Shepard is, therefore, female, and bears a distinct resemblance to me (if I were in shape like a space marine and not like a lazy gamer).
So Shepard is a girl. And I am not exactly known for flirting with other girls. In point of fact, I really prefer dudes. I married one! It works well for us. And so flirting with Liara is awkward, particularly with my husband watching.
It is an uncomfortable fact: no matter how aware or progressive you are, sometimes you're going to walk flat smack into the own brick wall of your privilege. At least I've had the good sense to know it for what it is!
The games that would drive a player into such a choice are few and far between, and more's the pity. For however mildly annoyed I am for feeling strongly guided into a Liara pairing (and I wouldn't be annoyed at all, except that 1. Kaidan is creepy and 2. I'm not playing solo), there are hundreds and thousands of LGBT gamers out there who are rightfully annoyed that they don't get the chance in other games. In fact, Mass Effect only presents the same-sex option to a female Shepard; a male Shepard has the choices of racist girl or exotic blue girl. And I resent that choice on male Shepard's behalf. M. Shepard should also have had the chance to be creeped out by and reject Kaidan.
I hear that BioWare has had some significant progress in this area in Dragon Age and especially in Dragon Age 2. And I know that originally Ashley and Kaidan were written as romanceable by any Shepard, and that it was scrapped. David Gaider's response to the "straight male gamer" is excellent and famous, as it should be.
I don't really have anything useful to add to the discussion, other than my own observations. This area's not my specialty and I'm more than happy to defer to others. We all know that diversity -- of all kinds -- in our games isn't where it needs to be. I've mentioned the several PAX panels on that theme I attended. In that light I'm mildly pleased to see this token choice put in, even if it does run into the hazy, muddy, troubled waters of "dudes like girl-on-girl."
Now if you'll excuse me... I need to go flirt with my husband's love interest. And after that, to Virmire...