The artificial, inward-looking, capitalism-friendly nuclear family is a fragile thing. It places two people in intense and prolonged intimacy which is neither natural nor sustainable. It places children in a position of total dependence on, and vulnerability to, those people. It undermines the natural family-clan-tribe structure we are evolved to live in. We are forced to live unsupported by a network and community of related people. A network in which every child is the responsibility of every adult. A social space which allows the development of close relationships with someone other than your 'official' partner. I'm not talking about polyamory here, but about 'spreading the load' of emotional suppport among people who, by nature, should be close to you. But capitalism wants us to find emotional support and fulfilment in consumption. It needs us fractured into small units so that we can't support each other and must work that much harder to provide individually ofr those who were onece provided for collectively.
Not that you'll believe that, of course. Some Christian type with your head up your arse I imagine.