It is realistic for people to have preferences. That's why white people marry white people more often than other ethnicities, and ditto for every other ethnicity. Whether that is 'good' or not is not really relevant, it simply is. If there were actually different sentient races (rather than just minor genetic differences among ethnicities) then you can bet people (of all these races) would have preferences as well, most of which would be prefer their own race.
I can see how some people wouldn't like it just because it does reduce the possibilities for the PC. But for myself I play 5 or 6 games (DAO I did 8 and on my 9th now, spread out over the years the games been out so its not a binge 9 DAO runs lol, and I did 3 full DA2 runs and 2 halfways), so I never really miss content that I don't want to miss (except for some easter eggs, but that's what youtubes for). So I'm fine with or without gating, but I understand why you don't want it.
Love your sig by the way 
A person's preferences aren't part of their character, though. Unless they're the result or expression of actual bigotry, they don't factor into a person's beliefs, behavior, or values. Zevran and Isabela are promiscuous; that's part of their character. They'd be promiscuous regardless of their orientation. Morrigan's a conniving ******(love her, but she is), and she'd be a conniving ****** regardless of her orientation.
A person's preferences are the entirely arbitrary result of the way their hormones flow. So unless the addition of preferences is the explicitly part of a certain racism on the character's part, it does nothing to enhance that character beyond giving them a random quirk.
I'd also point out that those preferences don't always equate to liking what's similar. I'm good friends with a white woman who only dates black men(she's less picky about the women she dates). So where's the human/elven/dwarven companion who's only interested in qunari because they find them exotic? Where's the character who isn't interested in the PC because the PC's fit and they prefer their lovers on the chunky side? Where's the LI who's only interested in mages because they can do that thing with the lightning? Why do these preferences always have to be in favor of "I don't like anyone who's different than me?"
The fact is that there is a vast array of preferences that make up the spectrum of sexuality. To even begin to give a realistic reflection of that would require far more LI's than we've ever had total party members. So any preferences given with such a small group aren't realistic, they're just random. They don't enhance the experience, they limit it.
Also, thank's about the sig; came up with it myself.