There's evidence polygamous cultures are better off than monogamous ones. Monogamy encourages sexual competetiveness.
"Extramarital Sex
I also examined the influence of extramarital sex taboos upon crime and violence. The data clearly indicates that punitive-repressive attitudes toward extramarital sex are also linked with physical violence, personal crime, and the practice of slavery. Societies which value monogamy emphasize military glory and worship aggressive gods.
These cross-cultural data support the view of psychologists and sociologists who feel that sexual and psychological needs not being fulfilled within a marriage should be met outside of it, without destroying the primacy of the marriage relationship...
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Available data clearly indicate that the rigid values of monogamy, chastity, and virginity help produce physical violence. The denial of female sexuality must give way to an acceptance and respect for it, and men must share with women the responsibility for giving affection and care to infants and children. As the father assumes a more equal role with the mother in child-rearing and becomes more affectionate toward his children, certain changes must follow in our socioeconomic system. A corporate structure which tends to separate either parent from the family by travel, extended meetings, or overtime work weakens the parent-child relationship and harms family stability. To develop a peaceful society, we must put more emphasis on human relationships."
BODY PLEASURE AND THE ORIGINS OF VIOLENCE By James W. Prescott
"In contrast with America’s male-oriented gender bias, Denmark’s high level of male-female equality allows for behavior that transcends the gender barriers set by less egalitarian societies...
...Denmark’s relaxed attitude toward male-female roles fosters an environment for untraditional relationships. Many couples are characterized as LAT (living apart together). These couples are romantically involved, but are not married. In Denmark, is not a pre-requisite for starting a family. Unlike in the United States, there is no taboo associated with having children out of wedlock.
Denmark also has a very high divorce rate, at nearly 45% of all marriages resulting in divorce. The lack of pressure to marry in combination with the social normalcy of divorce breeds healthy relationships, which could explain the Dane’s tendency toward public displays of affection.
The Danes’ non-traditional relationship ideals are further made evident in their liberal attitude toward sex. It is not uncommon for Danish men and women to talk about and even engage in sex in public places. During a dinner party with some Danish friends, I was shocked when one of the men turned to me and casually asked at what age I had lost my virginity. When I uncomfortably refused to answer, he teased me for being a “prude American.”"
Love and Relationships in the Happiest Country in the World
It's sad and unfortunate that many of the values we passionately cling to in America are the ones that are actually doing us the most harm.
Like the show "Extreme Couponing" but with marriage. 
