Wall Street is collapsing not because of bad mortgage debt or lack of capital or over-leverage. Those are merely symptoms. Wall Street is collapsing because it deserves to collapse; it needs to collapse in order for America to survive. The economist Joseph Schumpeter called it creative destruction, a system where outdated models collapse to make room for new innovation.
Wall Street of the past decade never really had a business model as much as it had a business creed: greed is good; leveraged greed is even better.