>You can use a condom.

Sure. Now. But monogamy and polygyny are a little older than condoms.

>Metamours [...] polycule

You're answering rhetorical questions which, incidentally, are not about terminology, but about legal and social mechanics. Knowing what a "metamour" is, says nothing about what the formal and informal responsibilities of the parties involved are or should be with respect to each other. My whole point is that not having to define such relationships and their expectations is a reason to forbid them culturally.

>You write a will.

How did that work before most people knew how to write?

>By the way, inheritance laws are messy already as they are.

That's not an argument in favor of legally legitimizing polycules.

>the reason is to reinforce division and oppression

I mean, I gave several reasons why historically either monogamy or asymmetric polygamy would have been preferred over symmetric polygamy, that have nothing to do with oppression.

>I'd wager that an entire society built on top of that would have no lesser chance at thriving than the one we've been born into.

Sure, maybe. Personally, I'm more of the opinion that cultural features are memetic, and that memes are not uniformly successfully propagated. If monogamous and polygynous societies are more common than polyandrous and polycular societies, it's probably for a reason.

> You're answering rhetorical questions which, incidentally, are not about terminology, but about legal and social mechanics.

Yes, that's what I've tried to imply. You name things, so you can discuss them in more abstract terms, so you can form a social & legal framework around those concepts.

> My whole point is that not having to define such relationships and their expectations is a reason to forbid them culturally.

>> [...] not having to define [...] is a reason to forbid [...].

Suppress the concept. "We don't talk about that."

> How did that work before most people knew how to write?

How did people enter agreements?

> Personally, I'm more of the opinion that cultural features are memetic, and that memes are not uniformly successfully propagated.

Agree. It's also how dictatorships rise. Another form of oppression that concentrates power and fires back at the group who have initially supported it. Another lose-lose.

Societies often overoptimize for a local maximum.