I'm wondering how many of the people oppose the homosexuality implementation are just homophobes.
*INCOMING BISEXUAL GAY RIGHTS SUPPORTER ALERT*
There's no reason not to put in variant ethics when it comes to homosexual acceptance. It's true that Dwarf Fortress technology doesn't extend beyond the 14th century (pump stacks that spew magma out over the countryside notwithstanding), but to say that society standards should necessarily be held to the same standards, I'd say no. For one thing, it just isn't our world (oh rly?). Homosexuals were persecuted in large part because of religion (you know who you are...), because of that funky little passage in a certain funky little book that said "dudes shagging dudes is totally balls, yo, it's not cool". Dwarves do not adhere to the particular religion which centers around that funky little book - the gods they worship seem to have more to do with caverns, earth, fortresses, jewels, children, and BLOOOOOOD than...anything the funky little book god had to do with. So that's a big part of the "no, Toady won't, because" with the rug pulled out from under it. All falling to the ground and breaking its nose and shit.
Now let's consider the other problem, which is just the fear people have of the unknown. I'd say it's fairly stupid to say that dwarves would exhibit the same immediate revulsion to homosexuality that humans (some humans, at least) have, on account of the fact that they're not humans. They're tiny, squat, ugly geniuses (who still manage to seal themselves into the caverns while sealing it off) who live underground, sup well on mushroom booze and kitten tallow roasts, and emotionally balance out at something like "okay" because on one hand, their entire family got killed by goblins, but they just stood next to a waterfall and admired an artifact chert table with spikes of donkey hair on the other. On that note, dwarves live in a world full of gory shit, rampaging monsters from the dawn of time, goblins sending sieges a hundred men strong to ransack their fortress and steal their children, statues of bronze that inexplicably want to fuck their shit up, birds the size of airliners, giants who want to grind their bones to make their bread, a night filled with demons, and kobolds who steal their beloved siltstone mugs. Are two men/women kissing or going on break in their shared bedroom at the same time really going to freak them out, you think? Really? Sieges don't even ellicit a thought from them, but homosexuals will make them go "AAAAARGH UNNATURAL CLEANSE PURGE WITH MAGMA AND SALT CARVE STATUES FROM THEIR OBSIDIAN-ENCRUSTED CORPSES HUGA BUGA BUGA". Right, man, whatever.
Which is not to say I'd oppose different civs - even different civs among a single entity - having different views on homosexuality. I'd try my damn darndest to make my own civ swing around from the standpoint of "no gays allowed" and drown every member of an anti-gay civ in a pit full of carp (modded to be made of adamantine and sever extremities with every bite), though, but that's just me.
I say, put it in.