I would be against implementing this if it was the only trivial personality* aspect that could be discriminated agianst. If elves could go to war with a mountainhome because their leaders eyes were blue, or their earlobes were detached, and most certainly not because their military is rich and squishy, I would have no problem with them going to war with the mountain home because someone is openly gay. If my legends mode were dominated by the spears of bigotry massacring gays with no one massacring for other comparably valid concerns, I would be uncomfortable with that.
*I say trivial, in that it is a small part of what of what a dwarf(person) is. A tall blond gay armoursmith is armoursmith, as far as I'm concerned
Look at the casus belli we have now.
We have elves declaring war over the fact that someone told a lie.
Surely, telling lies, cutting down trees, killing a wild animal for food, or mere elficide for fun are trivial enough reasons for war to already satisfy this idea that we should have other trivial reasons for a war.
Further, with the Personality Rewrite coming up, the main reason for war will be "The leader of the civ was expansionist, and thought he/she could get away with it."
Speaking of ancient history, did you know most ancient nations had no such thing as tax? At least, not for the actual citizenry, there was no direct tax, and they believed direct tax was "tyrannical". Instead, all the money in the earlier Roman coffers came either from annexing valuable mines (into which the State sent slaves they captured from conquest to work for the State's profit) or else through conquest, tribute, and taxes payed by non-citizen subjects of conquest. In fact, there was a "reverse tax" of sorts through the dole - the "Bread and Circuses" were state-funded means of distributing the tribute and tax the state placed on non-citizens to the citizenry.
I'm fairly sure that conquest just for sheer profit motive with a completely trumped-up casus belli, exactly as the Romans did it, will be the primary motivator of warfare.
I think we need to examine that 'trivial' things are not usually the cause of conflict in of themselves, but rather that they are typically an excuse where the 'real' reason will be bigotry, hence my example of genocide in response to killing a cow (which has happened in real life), where the 'trivial' reason was killing the cow, but the 'real' reason was that they wanted an excuse to kill those 'barbarians' in the next village over. This doesn't mean that the 'different-ness' of the other people won't be cited as a reason for why they deserve murder/war/slaver/subjugation etc, but it is rarely in of itself the 'spark' that sets off a conflict, instead a (often contrived) justification will be used instead. For isntance, the Elves might site a Dwarven Merchant lying as justifiable cause to invade, but the underlying reasons will likely be more complicated than that (why else would they invade a kingdom to punish the actions of an individual). For a real life counterpart, Pizzaro let the Inca emperor be given a bible, and when he (predictably) was not impressed and insulted it, his 'blasphemy' was used as a justification for attacking his entorage and capturing him, but hid a hidden motive, that being greed for power and wealth. there are plenty of examples of excuses being made for such behavoior that mask underlying prejudices and other motives.
In this manner, cutting down trees, eating animals, homosexuality, etc could all be examples of things which elves find culturally alien and disgusting practices among dwarves, and wouldn't necessarily be 'trivial' reasons in their mind-as they have ample reason to dislike them within their cultural context. All they would need would be an excuse such as a dwarf cutting down a tree in
their forest, or eating one of
their animals or makiing advances towards
their ambassador to have justification in their minds-as their previously disgusting (to them) behaviour has suddenly becoem a personal insult to the elves, etc.
Inother words, unless every civ has an ethics tag with HOMOSEXUALITY:ACCEPTABLE, I would expect the matter to be one of contention from time to time.
In other words, I would expect the history to say "The leader of the civ was expansionist, and thought he/she could get away with it. The conflict was over cultural differences B, Q, & R, and incidents X & Z were used as justification."
I think that cultural differences should contribute to a general favor/dislike relationship between civs that influences how likely they are to forgive transgressions or punish them. Large enough differences in ethics (ex UNTHINKABLE versus ACCEPTABLE) should be considered transgressions in their own right, and could lead to on and off conflict between nations.
As for the conquest for money thing, I recall hearing that Rome used the justification of 'pre-emptive attacks' to justify many of their conquests, under the reasoning that their enemies would invade them if they didn't invade first-but of course the real reason was greed coupled with a disrespect based upon cultural differences-which fits in quite well with the rest f my point.
Conflict/persecution/personalities/cultures etc all of these things are the result of a mosaic of smaller things which make up a whole. And while they may seem 'trivial' individually, they are all important in that they add up. Ethnicity, wealth, religion, sexual orientation are all items that are vital to the expression of the aformentioned mosaics, and as such, any good simulation of them should address them, which is why I think homosexuality (among the other things mentioned) should be implemented!