Even if all those are true, I still don't see the point. Anything that can be achieved through marriage can be achieved through other means. I don't understand what makes marriage so special.
I too would like to see marriage, as it is today, abolished. It seems far too much control for the state to have and no concern of the church. Even taken at a minimum, the present formalities are too much. Absent any children or claims on wealth and property, I see no reason for marriage and would discourage it.
Of course, a lot depends on what you mean by marriage. If it were merely breaking a plate over some woman’s head or signing the bottom of a piece of paper (to which would be added, as and when, the names of common offspring) and lodging it at City Hall, then, I don’t suppose that you would be too bothered. In many European countries, the people have a “Book of Life” in which birth, children, partners, property, addresses, are recorded. This could work if you are happy with the lack of privacy.
In its basic terms, marriage is responsibility for offspring and property. You may say, “Well, even if I had kids and even if I were divorced, I would still support them and remember them in my will” but we know others don’t and the responsibility for the brats’ welfare then falls on the state because, for some unknown reason, letting children starve to death is regrettably out of fashion.
As far as polygamy is concerned, as attractive (to men) as it might seem, it has difficulties; the distribution of genes is uneven and in small communities half-brothers and sisters will start to breed. Of course, from a genetic view, it doesn’t matter if a few people are polygamous/ polyandrous, the mix will still be good, but it would leave a lot of men minus a partner. Hormones would drive them to distraction and awfulness would ensue.
A society that is as populated and complex as ours requires minimum rules.
Society has grown up with marriage. That is not a good reason for an archaic ritual but my society has also grown up speaking English. English is difficult, illogically spelled and irregular. If languages were for sale, English would be a Blue Star bargain. There are far better languages to speak… so why don’t we abolish English and start speaking Esperanto? It would be the logical thing to do. It would cause confusion for about 30 years but after that, it would be plain sailing! So it is with marriage: our whole society and law has been ordered around it for millennia and a change would be painful.
So, as abolishing English requires replacing it with another language, so abolishing marriage would require something else in its place to maintain some order in society. That said, there are privileges of marriage that should go and privileges for the single and those cohabiting to be gained.