And, you might want to take note, at no point have I ever said anything glorifying marriage, other than to say what is needed to make a successful one. The fact that those attributes are uncommon should have been self-evident.
Let me spoon feed it to YOU:
... accepted social and emotional relationships which have formed the basis of human society since our species first evolved.
Do you see the word "marriage" in that sentence?
The social and emotional relationships which have formed the basis of human society since antiquity are NOT MARRIAGE, but then I wouldn't expect you to have picked up on that since, as before, you are reading INTO what I write instead of reading it.
Marriage began as nothing more than a way for men to try to make sure that their property or social status went to their OWN children. To do that, they had to prevent women from having sex except in a sanctioned setting. Multiple wives were okay, but they all had to remain sexually faithful.
In a pre-industrial, tribally structured society women could raise their children just fine with the help of their neighbors and friends. There was no such thing as an "illegitimate" child so there was no stigma attached to giving birth without a dedicated male partner to help provide for it. Like other apes, humans experience hormone-driven "love", or pair bonding as I prefer to call it, but it typically fades away after around 2 years, give or take, which is about how long it takes for a child to be weaned.
As humans became more civilized and acquired more belongings that they wanted to pass on to their offspring, women became more like property.
Many of today's marriage and divorce rules are still trying to redress the damage caused by that era; not always successfully, but they're trying.
A matriarchal society has a lot of benefits, but they have seldom endured because, looked at collectively, (meaning that there will be exceptions, but not a majority) men tend to be too aggressive to submit to being ruled by women. In a matriarchal society, though, where inheritance was traced through the females, who were also the landowners, paternity was essentially meaningless.
In our screwed-up society today, we have lost the safety net of a tribal structure, and children without two parents are at a huge disadvantage.
Some men are responsible enough to provide for their children because it's the right thing to do and they WANT to, with or without marriage, but too many are reluctant to do so, and for them the law has to get involved.