Like Hawkeye said: "Greed, lust, and greed. The three basic human emotions."A little late to the party here, but your diagnosis is on target. The problem is that no one has come up with a "cure" for the problem...pure capitalism is not...neither is pure socialism/communism. A mix seems to work but still has severe disparities...I guess that's the plight of human nature -- at bottom we all focus on self-interest.
Managed or moderated free enterprise seems most effective (and able to correct of abuses). That requires an electorate that is at least sort of paying attention and a ruling class that places the long-term good of the republic ahead of personal gain. Those are two really big caveats.