Morals, shmorals. The nuclear family is dysfunctional and that is the main reason for the failure of the institution of marriage. The nuclear family and monogamy are both unnatural to the human species. Our civilization is not based on the nuclear family or monogamy. It is based on control through hierarchy. Control through fear.
Beyond that, the nuclear family is new, and its chief advantage is that it's marginally better than single parenthood. For the vast majority of human history, people lived in tribes, clans, extended families,
derbhfine, what have you. It meant that if an adult died untimely, it was a tragedy, but the family would carry on. Contrast the nuclear family, where the untimely death of an adult is an economic, psychological, and social disaster.
Good for Big Government, Big Banking, Big Business, Big Education, and all the other Bigs, though. Keeps the adults in line and docile.
That's why power families, like the Bushes and Kennedys, still live in clans.
Ah but they actually do, the fundies within the Mormon church intermarry constantly, because there are fewer of them than the normal Mormons. So you have cousins marrying cousins, uncles marrying their nieces, then they lose track of who married who, etc. That's why there are so many tiny graves in the fundamentalist cemeteries. Then you have Warren Jeffs taking wives away from one man, giving her to another man, he ends up marrying her daughter, the next thing you know they have half siblings marrying each other. The worst part is that since they are all related in one way or another any genetic problems show up often.
Within the regular Mormon church there are problems as well again because the early church practiced polygamy, to today people who are not closely related still often have the same genetic problems.
Ah, but they actually don't. Polygamy is marriage between more than two people. Incest is marriage between persons too closely related to be allowed to marry (the exact degree of consanguinity varies).
They are two different things. Just because the Mormons practice(d) both does not make them related to each other. You might just as well say that abstinence from caffeine and incest are related because Mormons did both.