As social systems evolved beyond one big guy with a stick and the folks who watch his back, it began to become important to clearly define who was us, and who was them. Since fatherhood is always more or less a matter of report and opinion, and motherhood a directly observable fact, us was defined as born to one of us. The matter of fatherhood, once it was discovered, was a fairly important one, at least to men. The guy mentioned above was a man. The guy with the stick decided that he, and the folks who watched his back wanted to be sure that all the kids who were born of one of us were really one of us.
This is the human need at the time of Abraham. Women needed a social fabric that protected them and their infants reliably, even with accidental death of the man who fathered their child. Men needed to conserve their assets to provide for their own children, and each to feel confident that these were his own children. Within this framework of need, the religion of Abraham found an answer.
Families defined as one man and one or more women, with all the children those women had worked well for nomads. It worked a bit less well for settled people, and in fact, as the Jews settled, they practiced less polygamy, and more monogamy. Priests and hierarchical religious organizations find it very useful to be able to license marriage, by requiring sanctification of the estate, and in most cases, payment from the participants.
Societies grew, and collided, and absorbed each other, and times changed. Along the way, it seems that there were participants of monogamous relationships, of both sexes that found it to have benefits beyond the ones noted by religious authorities, or social pressures. The opinions of these people were passed on to their children, and the idea gained a lot of strength, both as a moral standard, and as model for a successful way to integrate individuals into the world of people in which they must survive.
The condemnation of those who practice different procreative habits is as reasonable as the level of authority of the condemner. In most cases, that authority is non existent. In the case of children, it is absolute. Every child must be protected by the rights that used to be conferred by the social and legal concept of legitimacy. With the technology of the today, every child is the legitimate heir of some man. Our law has yet to completely catch up to that.
Tris