"When a person stays with his/her mother, uncles and aunts, siblings and cousins, nephews and nieces there is tremendous moral, emotional and economic support that is hard to get in any other system."
I suppose that's true. Bleah, but most of my blood relatives are deeply steeped in the Mormon church and that atmosphere just wouldn't sit well with me. Nor would living in the heart of Utah. My two companions have similar issues. Brother-Husband has a heavily religious (especially Catholic) family members, and our Lady Hinge has very conservative folks. As for other relatives, there is a sister who nags other people all the time about how they should live their lives, and another sister with an obnoxious husband and two obnoxious kids. Not to mention many of these family members are spread far and wide across the country.
I think what the Mosuo have going for them is that they all live in close proximity with one another, have a simple farm life and haven't traveled widely so as to develop a taste for other parts of the world. In Western society, we largely get to travel around and choose the locality that suits our personality the best. One does give up the economic support of one's blood relatives when moving far away, but for some of us the trade-off is worth it. And there's the problem of how many of one's blood relatives would be accepting of one's non-monogamous life choices. My companions and I have few such relatives that would be accepting.
Heck there's also the problem of how controlling Brother-Husband's parents (especially his father) are, and how smothering my stepmother is. We kind of need to put a lot of distance between ourselves and them, just to stay sane.
But I'm not blind to the benefits of living near family (something I greatly missed while living in Michigan and New Mexico). So, I now live near my brother, his wife, her folks, her daughter, and her daughter's boyfriend. If we were in need of help I know we could count on them; and best of all, they are accepting of us just as we are.
Close friends can be like family too, but I admit I left 99% of all close friends behind me when I left the town of my birth. Back then it was a simple farm community, but now it's a vast, crowded suburb. All the quiet wild places are gone, replaced by busy streets and oversized houses. I no longer feel at home there. Feeling at home is something you can't put a price on.
It would be hard to transform all of Western society to look like the pastoral idyll that we see in Mosuo culture. We'd have to go back in time, and you can't turn back the clock. We need some kind of system that caters to the immense complexities of modern life. No longer can people take for granted what their mothers, uncles, aunts, siblings, cousins, nephews, and nieces tell them. We are no longer products of our ancestry; we have much independence, and the price of independence is sometimes loneliness. For those to whom that's a problem, a simpler, family-enshrouded life is needed, or at least a more intimate connection with the physical community that surrounds them. For my part, I consider myself content enough with the life that I have.
"Is this not an egalitarian and evolved society -- the dream of all social reformers?"
Ah but you see I am not a social reformer. Oh I'd like to see polyamory (etc.) gain widespread acceptance, but I don't lose any sleep over it. I am content to make small contributions here and there, to be in my own way the change that I wish to see in the world. It is enough for me to live polyamorously and show that it can be done without fuss or drama. I don't need to show people that small-scale agriculture (and freedom from permanent birth control) is the only way to go. I like the city (and modern amenities) as well (though I don't like how it's encroached upon my childhood memories).
But I suspect that even among social reformers you will find a wide range of desired surroundings. Some will be glad to go back in time, while others will remember how the good old days were also the bad old days (where things like polyamory were not accepted). And few (at least on this forum) will happily part with their computers ...