Leftists have never figured out, nor seem capable of figuring out, that marriage has profound biological utility. It is incredibly important to the success of the human species, and efforts to undermine it are having horrific and devastating consequences to vast numbers of people.
Yet leftists still think it is a “social contrivance”.
At the time leftism was first getting its philosophical legs, *corruptions* of marriage, mostly the dowry and arranged marriages, often of the old and young, were starting to collapse as failures. But leftists were convinced that it was marriage itself that was to blame.
They sought justification in the animal world, and still do, with such things as promiscuity, “cheating”, homosexuality and pedophilism. But they ignored the serious and deadly consequences of these things, emphasizing that “animals do it, so it must be okay for humans to do it.”
The utility in marriage comes from the different sexual prerogatives of males and females. The male prerogative is for their DNA to be in as many offspring as possible. The female prerogative is both to have the best male DNA for her offspring, *and* the unique provision and support of the best male provider to help her raise her offspring.
When there are more than a few males, the best DNA and the best provider are rarely the same male.
So monogamous marriage offers both the male and the female, and their offspring the best outcome. The male is far more likely to produce a child or children with his DNA. The female is far more likely to have good DNA but also a good provider for just her offspring. And their children are inclined to grow up on a success track of life, instead of a mere survival track.
But for monogamous marriage to work, it must be *respected* by others. This means that efforts to engage in adultery with either parent must be met with profound resistance, both by the couple and by society as a whole.
Importantly, there are far more people that *want* to breed than there are people who *should* breed. So there are biological mechanisms to keep those that shouldn’t breed from interfering with breeding pairs.
Things such as homosexuality, prostitution, post menopausal sex, abortion, self destructive behavior, and many forms of sexual deviation, are likely biological mechanisms to prevent non-breeders from breeding.
But the biggest threat to marriage and the species, by far, is leftism, because it is a direct assault on the success of the species itself.
You put post-menopausal sex in that list?