Human nature is inherently vicious and self-interested. A lone human being completely cut off from anyone else will become vicious and self-interested in order to survive.

This is just a default, though. The fallacy is assuming that this regressive primal state has any bearing on how human beings behave when they organize a culture together. The closest thing to “human nature” that one needs to worry about is the fact that people need to feel like they have control over their own destinies. That’s it. Everything else is extremely malleable.