That's royalty for you. Got to keep the bloodline pure.

Incest? You mean Wincest Anyways it typically royalty

LOL bigots! Should we sue for discrimination practices?!?! LOL a same sex marriage used to increase diplomatic prestige or something...

I'm sure they don't object to same-sex relationships, just to same-sex marriages. Ancient Greeks actually had a similar stance on marriage: Greek men would marry Greek women for procreation purposes, but ended up romancing Greek boys. Meanwhile, the wives would take on female lovers of their own. Nobody objected to this practice, so long as marriages created heirs.

Haven't seen it yet, but apparently Fable 3 has a system where one can enter into a same sex marriage and then adopt their bloodline.  Since I prefer to play with a female avatar, I thought that option was appealing.

Now that I come to think about all that... All women in my family are rather hot.... mmmh...

Inbreeding amongst royalty has a very long tradition.  Egyptian Pharaohs often married their sisters.  In Europe, hemophilia was common among many royal families.  The inbreeding cause the recessive gene for this to present as both parents had it.  The child ended up being a 'bleeder.'  (Wounds don't heal, or heal v e r y slowly.)  I don't know it this is where the expression "blue bloods' comes from. But it does explain why so many royals were insane. 

Do none of you find it just slightly disturbing how okay we all seem to be with this?

I, for one, oppose the idea, albeit on a purely biased and non-objective basis.

Sure, it's got the whole 'Realism' thing going for it...  But even that's half-assed in this regard.  Coming from a purely objective, game-play-related standpoint here, I have a couple ideas on the subject.

First off, give players a disincentive to inbreed.  Inbred children should have a trait.  First option to this end would be the trait 'Inbred,' which gives penalty(s) of some kind.  Exactly what, I can't say, nor do I want to even try.  Usually I'm all for examples and stuff, but I just spent a little over 9 hours finishing the current portion of my fan-fic and can't be bothered to think much harder than that.
Anyway, back on topic here...  Second way to do this would be to give Inbred children a trait, but NOT the 'Inbred' Trait.  ElanaAhova alluded to Inbred Royals having Hemophilia.  Give the kid a trait like that.  You could include any amount of traits, drawn from the wide variety of well-known side-effects of inbreeding.  Hemophilia itself could be one of them, and an (easy) example of what it would do is, "Damage taken takes N times as long to heal."  I can't say I'm exactly familiar with any of those oh-so-well-known side-effects so I can't give any more examples, but now you've got a jumping-off point.

Second, alongside either implementation of first idea...  Give an incentive to Inbreeding.  First, we'd need to change the 'Royalty' Heroes so we could instead give it to inbred kids.  Or, just give another trait that has the potential of making inbred kids worthwhile, whatever seems best here.

But I digress...  NO MORE VIDEO GAME INCEST!  =P

There is enough genetic diversity between first cousins to keep marrying cousins together for 10 generations before even the slightest defects start to emerge.  It's only really a problem for immediate family.  Or, like the European Aristocracy, when you do it for 200 years.

Due to defections, I was able to marry off two siblings. I did it just to see if I could, but didn't want to wait long enough playing the game to see their children. One issue this brings up, however, is the need to be able to get more information about the heirs when offering them for marriage.

All the defense of incest is ****ing gross guys.  Are you all head-****ed or something?  Good lord, ****ing your sister is wrong, and making babies with her is extra wrong.  End of the story.  This game isn't a damn history lesson, it's fantasy, and if you want incest in your fantasy, you are ****ing sick.  Please no incest, and please let us marry children to champions. 

Then we should have more options than just the royalty for our sions to pick from (which was the main cause of incest historically). Until then not only is it allowed, but it is encouraged.