I believe capitalism is the least-bad system we've created so far. Perhaps there is a better one, but as I said elsewhere the failed experiment of communism isn't one we should keep attempting--the cost in human lives is far too high.

But, to your other point, I think human greed is innate. I can't think of evidence that would suggest that greed is somehow cultural or learned. Boil the system down to the lowest common denominator, you find greed. Scale it up: greed. No matter what you do, you cannot remove human greed systematically.