Fundamentally, the aggregation of humans into increasingly larger groups seems to be more a product of cultural-technological pressures than of true choice. Towns and cities are a consequence of agriculture. People suddenly became static rather than dynamic, and being tied down to land and permanent structures is risky. Larger social groups help mitigate that risk both actively (a larger group to repel threats) and reactively (more resources and labor to recover from disasters). That led the the whole food surplus -> specialization of labor chain of consequence that we're all familiar with, which continues down into modernity. Fundamentally, we have organized ourselves into large coherent nations not because we desire it, but because these large cooperative institutions carry ten thousand years of cultural inertia, and because they have become a sort of prisoner's dilemma variant -- any nation which willingly and deliberately fragmented would be consumed both culturally and physically by its neighbors or by an authoritarian successor state. This is also, incidentally, why libertarianism, anarchism, communism, and related ideologies are fundamentally flawed: most of humanity's recorded history is of increasingly large populations submitting willingly to the tyranny of the few.
We don't group together because we want to, but because all of our ancestors have and because we feel it's necessary to do so for protection from abuse by other groups and internal tyrants.
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Look at it from another angle. The fundamental issue of breathing room can theoretically be solved by population control, but that is already in opposition to free will and to an extent human nature. The alternative is unlimited growth -- if every single human grouping incapable of cohabiting a space with another is capable of moving outward into their own space, that vastly reduces social friction because nobody is forced to live with people they are fundamentally incompatible with. That's one of several reasons why the development of a true spacefaring human civilization is a necessity. Not an "Earth Federation" or an interplanetary hegemony of any other stripe, but simply a level of technology in which life in and travel through interplanetary and ultimately interstellar space is a solved problem and trivially inexpensive.
Even setting aside the potential for functionally infinite living space if we crack the problems with long-term habitation of deep space and start building O'Neill habitats everywhere, the sheer number of potentially habitable planets in our galaxy alone pushes the problem so far down the road that it's more likely to be solved by natural evolution or bioengineering than for it to recur.
Population control is a temporary solution that should only really be employed until expansion is a realistic option.