The people who taught you what "human nature" is, have a vested interest specifically in you thinking that humans are naturally greedy cut throat creatures, because that serves their systems of exploitation and oppression which they need you to continue to participle[ate in not because it's fact.
Beyond that, your argument is 100% appeal to tradition, and you not being able to imagine existence outside of the social constructs that have been around in some cases for a mere couple of hundred, in other cases for, at most, 4-5 thousand years, doesn't mean it isn't possible, only that you've been indoctrinated well enough in to believing that is the case.