FWIW I agree. My own idea (probably not original) is that the State should get out of the “marriage” business entirely but rather have something like a “family corporation” registry process instead. I’ll admit that I’m somewhat influenced here by ideas from my religious system whereby there is a marriage contract which specifies rights and obligations and penalties for dissolving the contract. This would allow same sex and multi sex families all to be equally happy and miserable.
Id go further in borrowing from Jewish law in that the articles of family incorporation would have to specify limits on how the family entity could be expanded, what “voting shares” are required for an expansion or contraction. In Jewish law, a man was limited to a maximum of four wives and to even take on one after the first it was required to provide proof of being able to support n+1 usually providing her with her own household or the equivalent. Of course allowances should be made in civil law for however the contract should be structured for any living arrangement, etc.
To me that is a bit of a red herring in regards to legal polygamist unions as not all hetero or homosexual unions are in any way guaranteed to be free of those same issues.