I'm still waiting for a good argument against plural marriages as long as it is between consenting adults...la
Suppose 10 men and 10 desirable women find themselves stranded on a deserted island. Suppose 2 of the men are much stronger than the other 8 and also have control (at least in the beginning) of all of the weapons on the island. These 2 men decide that they want all of the women for themselves and so they take 5 women each and warn the other men of dire consequences if they try to interfere. Violence is an almost certain result in such a situation.
Do we really want a society in which marriageable women become a scarce commodity? Look at Saudi Arabia, where the richest men take 4 (or more wives) and many, many young men are left without access to women. Their only hope is to go on jihad and maybe get 72 virgins from their moon god after they blow themselves up.
Many of those wives are imported.
But your theory supposes that every man always gets a wife, and that ain't true anywhere you go.
The powerful in life almost always get more than the weak and that is just the way it is. And should be.