The Inbreeding is massively less a chance of bad result than many take with their ofspring when they have genes that cause all sortf of nasty genetic illnesses at 25% or more chance when this is under 10 for one generation.
Note having a genetic sample after embryo X days old can tell you to abort or not and with genetic editing making major advances the genetic risk goes to zero. Ancient Egyption practiced multi generation incest and yes some father/daughter like Rameses the great who married all his top daughters. Like most ancient civilizations they practiced infantcide where they kill children with defects. And incest created the German Shepherd as breeders have used the incest makes good traits occur just like bad ones so you kill the bad offspring keep the good.
Base +6, diddlyding -21, lostlegoman -9, Falconartist -6