Selfishness and greed are not "human nature." Self-preservation is human nature. In a capitalist society that rewards ruthless competition and leaves the poor to suffer and die, this drive for self-preservation manifests as selfish behavior at the expense of others. If we lived in a society that punished selfish behavior and rewarded actions that benefit the collective, selfish behavior would be much less common.

I think the core element of our capitalist society that fosters selfishness is the utter irrationality of our economic system. You can do all the "right things," plan out your life in the perfect way that's *supposed* to lead to success, and still get screwed. Even if you're living a comfortable life, you could lose it all at any moment for reasons completely outside of your control. No financial cushion is ever big enough.