= new reply since forum marked as read
And the reason that monogamy has been promoted (and the reason there's more stigma for females who step out) is to insure that a man was spending his energy to raise his own child, not someone else's.
This is the nuclear family view of family, rather than a larger, extended family view.
As a lot of people here know, one of the best examinations of the origin of monogamy came from Engels - within the context of looking at female subjugation within societies.
Engels states that the nuclear family model, and the pretense of monogamy for all marriage, and tracing children through the male line is also the origin of prostitution - b/c females are divided into those who are under the name of one male for financial survival, or those who earn money by selling sex. Historically, prostitutes were oftentimes women whose husbands had died, etc. and they had no source of income. This still goes on among poor people in just about every society I can think of.
But the issue comes down to males as uncles or males as fathers as their role in a family - so you're just seeing things as an uncle. 
This is also the way that primatologists look at homosexuality within humans as a genetic factor that was positive - those who weren't attracted to the opposite sex wouldn't be dealing with their own kids, and they were helping out with those whose biology meant that they would. The benefit is through carrying on the extended family gene - in terms of the selfish gene issue. Whether that's true or not - I think the point is that this makes sense when you're not looking at a nuclear family as "the" unit of society.
Since our society has so few protections for women who place childcare before building a career - women who have chosen this route have to contend with sexual jealousy. they're afraid they'll lose standing and income in society if their guy decides to have sex with another woman. This is why so many of them are religious - they get a REALLY big guy on their side. But men have sexual jealousy, too (my ex was jealous for no reason.) Or rather, the reason is that they don't want another guy's kid around, and don't want to lose their kids since our laws favor kids going with their mother for the most part.
I've said, a lot of times, that I wonder what female behavior would be like if they didn't have to worry about their economic survival or that of their children if all women, and men, for that matter, knew they would not suffer by not adhering to the status quo. Since lesbians deal with the same income equality issues as other females - I don't know if they offer insight on this issue since we're all in a "trying to survive" mode. But they don't deal with the paternity issue, so I think they do have somethings to say about some aspects of committed relationships.
I know that one criticism of the gay marriage push is the idea that monogamy, etc. doesn't need to be a part of how one is acceptable to society. For me, I view the religious opposition to "gayness" in general as a tell for the disgust for femaleness - b/c of the stereotype of how a male treats another male in a sexual relationship. I find it offensive for males to view my desire as disgusting if it's placed in the context of two males.
Monogamy is just easier when you have kids and are trying to live in such a way that you can afford to retire, etc. etc. But the reality is that even within monogamous relationships, women, esp. religious women that I've known, read romance novels and fantasize or just simply get aroused by the idea of others having sex - tho they would never see it in those terms... voyeurism as a turn on. So, it's not "cheating" if you don't make bodily contact with someone else, I guess.
I think the biggest problem with monogamy is boredom. The trade off is in other aspects of the relationship, and the relationship of parents with their children. But, even within monogamy, I think both women and men get aroused by others - they just take that feeling back to their marriage bed.
I don't care what someone is doing or not doing until they start telling everyone else what to do - or try to pretend they're doing something they're not, and this somehow makes them "good" in comparison to, say, someone who did the same thing but also decided not to stay with a partner.
can relieve the boredom. Just throwing that out there, and that is something everyone decides to do
Unless, come to think of it, for me it involves a male: Eww.
Your mileage may vary.
I'm no longer married, fwiw.
I've never met anyone, since I was married, that I'd want to commit to, so this is all abstract for me at this time.
