@Flyingpantsu Just because it was practiced by past civilization does not mean it is acceptable. Afterall, murder,human sacrifice and slavery was practiced back then.
Inbreeding can cause the demise of a civilization. Inbred rulers does not live long or sterile thus a high chance of succession conflict. Some develop madness a trait deadly to the populace.
This has reached an ignorant level on incest for Japan. The author cannot be serious in thinking that it's somehow fine if it's tradition, right? There's natural and biological reasons as to why incest is just not right.
Hey, everyone who is worried this will turn to shit, don't worry. I can assure you it won't go down hill from here.
Abel is completely against it and even decides to run away when he has no other option. You'll see this next chapter, so you can chill out. I read ahead in the raws and it's not going to go the incest route.