Oddly enough, finding times where incestuous marriage was considered acceptable is easier than finding times where homosexual “marriage” was considered acceptable. After all, Abraham’s wife Sarah was his half-sister, Rebekah was Isaac’s first cousin (daughter of Abraham’s brother Nahor), and Rachel and Leah were Jacob’s first cousins (daughters of Rebekah’s brother Laban). Even today in many parts of the world, marriages to first cousins are quite common.
It’s generally been parent/child (and step-parent/step-child) marriages that have been universally frowned upon (along with marriages between full blood siblings - not so much for half-siblings or siblings by adoption). The main reason for this has to do with the parental authority a parent has over his/her children, even when the children have grown up.
Regardless, this doesn’t mean such relationships should be legalized.
