This is probably a good place to say "wow, I certainly should not have used the words 'the ideal' but should have used the words 'an ideal' instead."
I agree that there is not one ideal system that will work for everyone. A different way to express what I originally intended might be this way:
First, by "ideal" I mean a cultural belief that something is good and valuable and right.
Second, I would propose that openness, honesty, flexibility, sharing, community, compassion, and growth would be good "ideals" to espouse in a culture.
Third, those values can support monogamous sexual relationships or polyamorous sexual relationships. I would love to see our culture develop in a way that supports a range of alternatives to the monogamous nuclear family household. Such a culture, and such a society, might support extended family households, communal households (which might contain monogamous pairs or people living in a range of nonmonogamous relationships), individuals in their own households who link together in looser or tighter networks...
Now, could we do this while still giving legal privilege to the monogamous nuclear family household? I suppose so. But I hope we wouldn't.
...because public space really matters!
Elizabeth