I think the difficulty of this is that whatever it meant in the ancient past is not necessarily valid today any longer.
Very basically marriage is a promise to be together forever.
It was necessary in the past for families as, starting eons in the past up to years in the 20th century, women had little rights and were often tied to the men around them (in several cultures even). In some cultures they had to obey their fathers first, then their husbands, then their son and if all of those passed away, their brother. Furthermore women where handled by their virginity. A woman that was not virgin anymore, was (and sometimes is still today) considered impure (and maybe worthless).
Marriage was a protection for women and their children because if the promise had been made then it was more difficult for them to be forsaken and also to be tormented by other men.
If the "family founding" was just an "idea of the moment" the woman might get pregnant and suddenly the man might decide to leave her just because. A pregnant single woman at ancient (till more modern) times was probably considered a severe disgrace, not to mention that it would be close to impossible or at least socially really hard to raise a child or more on your own. Those children would, too, suffer a huge impact of the social standing of their mother.
Besides this marriage was also for expanding and keeping power, for gaining prestige and wealth. A cleverly arranged marriage could bring a family a lot of honour while the wedded woman (and man) were just the pawns in the game.
So at least I think it was not really for reproduction or at least not for reproduction only - because you can reproduce without marriage - but to keep the given social norms stable and to influence social situations, from a minor household up to a whole kingdom, a bonding of humans had to be made.
However this cannot be applied in at least our Western society anymore.
A single woman can (more or less) raise children alone and she is not considered a disgrace or worthless person (at least ideally). Ideally, there is no social rule than women have no freedom and need to be obedient to their husband so that they'd need a marriage to tie themselves to them as a security.
And since inherited power has been removed with democracy political marriages are at least no official and expected game of our society anymore.
Don't want to be too biased on men though as their situation has also changed: They don't need to present enormous wedding presents to vow for (or "buy") their brides, they too have more freedom to choose a partner and not have to tie her(him) to himself etc.
The idea of a promise to stay together forever has stayed though but due to our society there are new premises and possibilities tied to it.
So since the social norm has changed the social norm for marriage has changed, too. You cannot apply an ancient marriage concept that comes from a totally different society on a modern society whose binding behaviour and gender models have changed drastically.