I think it is based on God and the Bible apillar. Who gives a spit about “science” of ethics? Get real.
“Gas is higher in Europe than it is here.”
“The European leaders all have mistresses but America is so far behind the times.”
“It’s okay for siblings to marry. This used to be common practice.”
See how it goes?
There’s nothing in the Bible about not marrying your cousin, yet we have a taboo against that. So it’s not all from the Bible.
Abraham and Sarah were brother and sister.