The unsustainability eating away our economy isn’t a function of capitalism’s rapaciousness, it’s a function of debt. While debt has its place in any good economic system, it’s use is also a two-edged sword.
It’s supposed to be used when you can properly price the risk of an investment and borrow money at a rate lower than the investment’s rate of return, in essence sharing the profit of the enterprise with the person who loaned you the money.