Let's say you were forced to move to a new country, where the law was that you had to marry, have sex with, and carry children with (magically possible) someone of the opposite gender that you're currently attracted to. Or say it was animals. You had to marry animals. Would you still say, "You can't carry on with your old country's way of thinking, this is a new country. You have to adapt to their common sense. Also, you'll have magical werewolf children." I'm pretty sure none of you would be okay with that. His response isn't unreasonable. I'm pretty sure you'd also like to leave this country with its weird common sense that disgusts you to your core. Sounds to me like lots of you just want to see your hardcore brother-sister fucking fantasies realized, in which case, go watch some porn and leave these children out of it.