If you look at the communal evolution, or lack thereof, you find that it keeps shrinking further and further. Communities of trust and devotion are getting smaller and smaller, there are fewer people to rely on.
A long time ago, anyone in a small communal would typically assist with anyone else. Who can you trust? "Pretty much anyone here!"
These days, who the hell can you trust? Marriage in a legal system is irrelevant, and really any sort of paper contract and adding property to the pact seems to complicate everything, but it is kind of necessary I suppose since that is how our society is modeled. As for my potential wife sleeping with anyone she likes, hell no! This isn't a thing about power, it is about me not wanting her taking risks that could impact me. And I would offer the same in reciprocation. I don't go and sleep around for a couple of reasons:
1) Risk of STD. This is a HUGE risk. I don't want any of that crud. I don't want to have to choose between sleeping with my spouse or take the risk of catching something because she caught it. I don't think the benefit of a day of pleasure justifies that risk unless there is more to the equation.
2) Risk of attachment. Lust is closely related to love and it is common for one to lead to the other. The more individuals you add into that equation the more risk for complexity in a relationship. Suddenly Joe or Jim or Moe that your spouse slept with for fun now needs something and your spouse feels inclined to take from the resources you have pooled in expectation of supporting your immediate family in order to support someone else that you may not even know/like.
3) Risk of idealization. It is SO common to see the grass as greener. If you sleep around quite a bit then there is potential to have better chemistry with someone, even if temporary, and thus make the inference that dedicating yourself to that person would be more beneficial to spend the majority of your life with. Arguments happen, and it is perfectly reasonable to say that during some temporary argument the significant other will feel so inclined to leave for this other 'perfect' mate. So all of the sudden, the kids are crying, the spouse is leaving, and you know it is all bullshit and things most likely won't work out between those two. Even if it does work out for them, it is still a fairly significant loss for yourself and the children, unless you are a shitty parent, then it is just a loss for you.
4) Risk of impregnation. Ok so we all know what sex is biologically for, right? Of course the pill will help ensure this doesn't happen. If you are used to sleeping around, and you happen to not be on the pill right now, then you go sleep around and woops! condom didn't work like it was supposed to! There is always risk with this. I don't want to deal with complications of having to help raise the love child of Joe/Jane and the spouse.
Now, if this were in a small community where everyone assisted one another, then none of that would be a big deal, besides STD. But it doesn't work that way, and so that increases the implications of the risks.
If by some amazing contract it were possible to avoid ALL those risks (not just saying "yea I can do that" but rather ensuring it, because talk is cheap) then I suppose I wouldn't have much of a problem with it. However, the overhead seems SO steep and it seems so unlikely, to me, that it is even possible that I just dismiss the notion entirely.
I admire your clarity.
I took a marriage and families class and that statement upset and so did a lot of other things in the book we were expected to learn from. Like "true love" doesn't exist it is just a common myth. I don't find it unnatural to establish a monogamous relationship with another human being.
And you are right about the kids aspect. The family can be broken in pursuit of a "better lover". =/ This angers me with the 50% divorce rate or whatever the statistic is now. No one is happy because of that "idealization". No one wants to try to work things out anymore it seems.