Ultimately, human nature derives from evolutionary biology, which in turn comes from fundamental aspects of game theory. That's why, if we contact aliens, I don't think they'll be as alien as some imagine: their society will be driven by the same fundamental generic imperatives that constrain our own and should be recognizable. We're primates, not pure energy beings that we can reprogram at will.
> Are not changed men the product of changed circumstances?
And changed circumstances also arise from changed men, all the way back to homo erectus. Human nature is mutable: genes and culture co-evolve, but with time lags far longer than a few generations that utopian social engineers imagine. Human nature does change over long time scales, but for our purposes, it's immutable.
Might some alternative organization of society do a better job matching our immutable-on-short-time-scales human nature to our technological environment? Sure: it's conceivable. But there's no reason to suppose that the particular forms of societal reorganization that utopians advocate fall into this category.
Historical evidence, on the contrary, suggests that collectivist societies are actually further from the optimum than our present structure, which we arrived at through millennia of trial-and-error and free choice. It's a unique kind of hubris to imagine that you can do better than the distributed choices of billions over centuries.
You're right: sociologists have "looked into" societal reorganization. So have biologists. When we listen to the biologists, we get elegant theories that make sense of both our observations and our failures to remake societies for the better. When we listen to the sociologists, we get the holodomor.
> To "human nature" I say firmly: human society.
We are not blank slates.