I will throw in the small fact that first generational incest has less of a chance of any birth defects than any person of a large variety of disabilities having children does, yet those people are still allowed to have as many children as they want and take that chance. The reason societies are against incest is not because of that risk, as it isn't significant enough to warrant that, it's always some other moral stance. The fact that the player character in this game is a magical fucking dragon does also completely invalidate any genetic risk, so that argument is entirely nullified. Also it's a porn game so it doesn't matter.