This banking system (the "shadow" or "parallel" banking system)--repo based on securitization--is a genuine banking system, as large as the traditional, regulated banking system. It is of critical importance to the economy because it is the funding basis for the traditional banking system. Without it, traditional banks will not lend and credit, which is essential for job creation, will not be created.
[T]he crazy facts are these: bankers now borrow from their customers and from taxpayers. They are effectively draining funds from household bank accounts, small businesses, corporations, government Treasuries and from e.g. the Federal Reserve. They do so by charging high rates of interest and fees; by demanding early repayment of loans; by illegally foreclosing on homeowners, and by appropriating, and then speculating with trillions of dollars of taxpayer-backed resources.
Regulate shadow banking more tightly, and you probably have to also provide government backstops. Shudder. Try to shut the thing down or restrict it and you suck credit out of the system, credit which much of the non-financial "'real" economy uses and needs.