The indigenous and enduring version of hierarchy, is and will always be family.
Practically yes, probably true for at least the next few centuries. In my personal politics I support the social support of family development by means of financial help and so on, curing alcohol addiction of parents so as to create better role models, etc. But there is no theoretical reason why this will "always" be so. Cockshott gives a good description in his book "How the World Works" of how societies changed from matriarchies (the "longhouse" that the internet right wing often complains about) to patriarchies partially as a result of the agricultural revolution, what he calls a "trophic level descent". Another trophic level descent could well disrupt even the somewhat vestigial aspects of the current reproduction relation and its consequences.
For warfare to exist you need something to fight over. Whereas warfare in pure hunter-gatherer societies seems rare [Fry, 2007; Ryan and Jethá, 2012] it has been common in societies with either herding or at least some form of agriculture. It is clear that once cattle or other beasts are herded they can be stolen, and can be the object of a war party. But fighting is not limited to what Smith called Nations of Shepherds, formidable as these have been.15 Nations and tribes that combine some hoe horticulture with hunting have been warlike. Why?
According to Meillassoux [1981] the motive for the conflict was the capture not of cattle but young women. Pure hunter-gatherer societies are nomadic, with no fixed villages, and mobility of people between wandering small bands. Agriculture ties people down. He argues that the initial form of family in the transition to agriculture is the matrilocal, which means a society in which adult women stay in their mother’s home or community. Insofar as there is mobility between communities, it is the men who move, seeking wives in other communities.
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This leads to endemic hostility and suspicion between communities. Men acquire the social role of warrior both to abduct women from other groups and to protect their own women. Such societies may remain matrilineal, with children being brought up in a relatively communal household with their uncles playing what we would regard as a paternal role. There may be no system of strict monogamy. But the beginnings of the collective dominance of men over women exist. Men as hunters and warriors develop ideologies that represent them as protectors and heroes and which justify relegating women to what are presented as menial horticultural tasks. In particular the abducted women, cut off from their own community, are likely to be in a very subordinate position.
Today, IVF and egg freezing already mutate this relationship somewhat. Sheep have already been reproduced using both cloning and artificial wombs. The right wing's response to this has generally been to complain about it or point out (not necessarily incorrectly) that this is inferior to the Real Deal. But then you have something like a society which uses these methods to create "cheap" soldiers, for example, capable of conquering others that stayed with the "old way". So pearl-clutching generally puts one at a disadvantage. Just as production of energy has largely been socialized in the form of electricity, sexual reproduction has already been socialized by technologies like birth control, the medicalized abortion, "One Child Policies", most recently primitive forms of embryo selection. There is no reason to think that sexual reproduction will be untouched. Even if we realized that some of these things (such as birth control) have negative consequences.
The families with the strongest cohesion become communal pillars of stability.
Sure. But it would be wrong to extend this relationship wholesale to the present day, in which the size of communities, for example, is dramatically expanded by roads, internal combustion engines, telecommunications. To do otherwise would appeal to the naturalistic fallacy. But I don't think spending many hours a day acquiring food (as a male) and collecting water (as a female) is the ultimate calling of man. Humanity itself is inherently technological insofar as our brain was made possible by the use of the spear and such for hunting. And so the idea of the inherently natural is not only fictional, but literally deficient as a method of fighting conflict, which is one of the most important pressures on a social system.
I think your characterization of the rational "social contract", in which the peasant "rationally understands" how hierarchy is good, is not correct. Julian Jaynes, in his book "The Origin of Consciousness in the Breakdown of the Bicameral Mind", gives a good characterization of how the first "super-hierarchies" of God-Kings in first agricultural states in Iran and Iraq were religious structures enforced by things like replications of the God-King figure in a dedicated room in every home.
This reality is cut as deep in the brain as the need for sex and food -- it can never be replaced. I hope communists can see that even they would need a leader in history past, to trust and follow when revolting...
To your point, the "Great Leader" meme is one of the most endemic ones in Communism. Mao Zedong achieved success with the Red Army because it was highly people-oriented, and so people helped and trusted it.
This isn't incoherent, but somewhat conveniently for me, food production is a pretty good example of what Marx and Engels describe as "dialectical materialism". And as Cockshott puts forth in the above book as well.
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Going lower in the system unlocks dramatically more energy. Hence the value of Sugar (produced by plants) in Peatarianism.
So I don't see why sexual reproduction relations would necessarily have to remain fixed.
In general, one aspect of Marx that you seem to overlook is Dialectical Materialism. You gesture at "dialectics running their course", but generally don't consider actual change in productive and social relations to be possible, you instead invoke the past as an example of what is correct. This is an unserious perspective as their system was completely different from ours today, just as theirs was different from the prior one.
Is taking exogenous progesterone (which is synthesized using organic chemistry techniques from yams) natural? No. Neither are the highly productive varieties of fruits that Peaters benefit from today. Nor the Nitrogen Chemistry which makes it possible to grow so many plants anyways. And yet these things offer an advantage. To reject them on the basis of naturalism would be suicidal in the face of real conflict in the world.
It is not necessarily warm and cozy to contemplate such realities, the little cliches that make up life as we know it today one day becoming limiting factors on existence. But we must make peace with their expiry (when it comes, which is not today) and find the good in the real at all costs. There is no going back.
Postscript: I suspect that when embryo selection becomes standard procedure in the socialized sexual reproduction system, only then will the medical establishment realize that genes aren't all that. Down Syndrome may well be eradicated, which I welcome. But something like "selecting for intelligence", people will eventually realize that doesn't really work. And so the paradigm will be questioned.
By the time soft-engineering slithers out of its box into yours, human security is lurching into crisis. Cloning, lateral genodata transfer, transversal replication, and cyberotics, flood in amongst a relapse onto bacterial sex.