Glass-Steagall

After the Great Depression was kicked off by the 1929 stock market crash Congress passed some laws intended to prevent a recurrance, ever again.  One of the contributing factors to the 1929 crash was big banks playing the stock market, with depositors money.   And in the 1930's Congress passed a law preventing banks for buying and selling stocks.  This was the Glass-Steagall act and it remained the law of the land for 60 years. Banks hated Glass-Steagall 'cause there is a lot of easy money to be made in the stock market, particularly if you have a lot of money to invest. It took the banks 60 years of solid lobbying and "campaign contributions" to finally repeal Glass-Steagall some time during the Clinton administration. 
   And now after Great Depression 2.0, kicked off by banks making dumb ass mortgages, people are calling for some regulation to curb big and brain dead banks from crashing the economy.  Bernie Sanders is calling for reinstatement of Glass-Steagall.   Actually this is a fairly good idea.  Banks primary purpose is to finance construction and house sales, and finance business activity.  Buying and selling stocks just soaks up bank assets and does not contribute to economic growth. 
   The other thing banking needs is some incentives to write decent mortgages.  The "Ninja" mortgages (No income, No job or assets)  caused the crash of 2007.  A mortgage must not exceed the real market value of the property, in fact the buyer ought to put up 10% or so of his own money to buy the place.  And the bank needs to see that the borrower is gainfully employed and is making enough to make his monthly mortgage payments.
   One way to make this happen is to require that the bank that issues the mortgage must hold that mortgage to maturity.  If the bank knows that it will b holding the bad should the borrower default, they will be fairly careful not to write mortgages for untrustworthy borrowers.