> Personally, I think we'd all be a lot better off if we adopted open and polyamorous relationships in a large way. They're better for resource-sharing and avoid the problem with thinking that your partner has to satisfy you in every way.
I agree entirely with this, but just as civil rights and legalizing recreational drugs took forever (and is still ongoing), it's going to be decades of effort to dismantle the societal expectations of marriage while still enabling the benefits that come/came along with traditional marriage (legal, financial rights).
Relationships are hard enough with just two people, adding more people doesn't make it easier, so you have to provide resources to help cultivate that stability society wants to express (insert diatribe about lacking mental health funding here).
EDIT: Regarding raising kids in a poly family, "it takes a village" [+].