Well, that was my point. How did humanity multiply from Adam and Eve without massive incest? And since incest was inevitable and required for the expansion of mankind, what is wrong with it now?
And spiritually, there had to be a first human. The animals don't understand that there is a God. There had to be a first creature who could see that there was a God. And that was Adam. To worry about incest when a truth like that is being given to us is looking for flyshit in the pepper.