MyLittleBrother
incest has only been considered taboo in last 1000 years because of the bible. before there has been many cases as humans were sparse and one would not see another human even if they traveled. also science has proven that there is no negative to incest as long as it's not done more than one generation more than a generation leads to genetic degradation which usually leads to all kinds of deformities and mutation usually retardation of all kinds.
Some say we are all descendants of an incest relationship since Adam and Eve's children married together. Either way, I never get why incest is even a bad thing in a cultivation world. The reason it's bad in our world is the genetic problems it can create. But for God like cultivators that can alter their gene and everything. It should not matter.