That's a pretty terrible argument. Yes, it's reality and 'to be expected'. But that doesn't mean that people who aren't in the majority group should be expected to just "roll with it". In fact, if anything, the fact that it's just played off as 'expected' by the majority is exactly why people in the minority should challenge it to some extent.
I agree that I'd like to see more mixed race human couples in DA. It's not uncommon to see in Mass Effect, but there aren't that many that I can think of off the top of my head in DA. Outside of Vivienne and Bastien, obviously.
While you might not understand the writer's intention while experiencing it the first time, it doesn't negate that intention altogether. Particularly when they make that intention public. You can choose to ignore any clarifications on intention if you choose to, but it doesn't mean that they don't exist and are, in fact, reality. In this case, you might have perceived Anders as straight, but he was always bisexual. Perception is not, in fact, reality when it comes to situations like this.
I have seen a ton of complaints about Steve and Kaidan in ME 3 as well. Neither of them have 'forced' rivalry points/consequences.
I think it's interesting to look at the trends across the characters. There have only been 8 gay or bisexual male LI's in Bioware games ever. (To put it in perspective, there are more than that just for straight men in SWTOR alone....) Of those, there are regular complaints about how 'forced' the interactions with Steve, Kaidan, Dorian, and Anders are. There are not those same complaints about Sky, Zevran, Bull, and Fenris. To me, the difference is that the first group is the group that has the 'audacity' to openly flirt with male characters without being prompted by the PC. That's the issue. What's being 'forced' is simply the acknowledgement that there are men who are attracted to men. We don't see the same complaints about Fenris because he doesn't talk about his sexuality at all if you don't romance him. And you don't see the same complaints about Zevran because he actually asks for permission before he flirts with you (outside of the guys who agree to have a 'backrub' from him in their tent and then get up in arms that it's not just a 'backrub'......smh).
Basically, my point is this: what's good for the straight goose is good for the gay goose (since ganders aren't really relevant in this metaphor.....). If it's okay to have a bunch of lady characters flirt with male PCs without prompting, then it's okay for male characters to flirt with male PCs without prompting too. The only people who should have problems with male characters flirting with their male PCs are the people who have problems with any character flirting with their PCs. Otherwise, my advice to them is suck it up, buttercup. At least that's my view on it.
Actually a gander is a male goose 
That aside, the problem with Ander's so-called flirt scene wasn't that he was firting with a dude, despite all the silly complaints about that. The problem was that you were given 2 options, which, to a new player, appear to be saying
initiate a romance or </3 abandon all hope for a romance, shortly after meeting the charcter. Add on top of that the fact that Anders was possessed and clearly off balance emotionally.
Contrac that to Isabela who also flirts with Hawke. She suggests Hawke meet her in the Hanged man for 'company'. A suggestion that was used in the demo as a clear ploy to sucker in hormonal teenaged boys.
To compare to Anders scene, Isabela would have given 2 options (and 2 options only):
Giggity, see you there or </3 Get a way from me you skanky pirate.
Ander's scene would have been improved simply by giving the player more choice in responding. If they had, no-one would have complained.
That said, I don't really understand everyone's praise on how Bioware handles 'diversity'. They kind of suck at it. Plainly LBGT people were the flavour of the day for this game, which is fine, but they could have still had all that content and still had a more diverse world than what they did.
Funny thing is, everyone sees the game as reflecting the majority genetic makeup of America, which is great for Americans, but what about everyone else? A full third of the population of the planet is not represented, but hey, we have 2 gay characters! Look how awesome they are!!
So we have 2 gay, 2 bi characters, a scattered few references to LBGT issues. Great, but where are the asians? How many people in this entire thread have even brought this up? I'm guessing not many as Asians don't make any noise about it. Add a few few cameos of women in power, so no need to have very many women as any of the inner circle! One black character, one of each thedas race, and the rest are white dude(ette)s. Yeah real diverse Bioware (clap clap)
As for mixed race relationships, I don't see why this is even an issue. Are Americans really still so hung up on mixed race couples? I thought that went away in the 80's.As someone who is in a mixed race relationship, I really didn't notice, nor do I care if a game has mixed race couples in it. I did notice, however, that I can't make my wifes face in the CC due to it being pretty much impossible to make any character look like anything but Caucasian or African. (yes I've seen peoples attempts and was less than impressed.)