"The Fed couldn't drain its reserves where one third of roughly...

"The Fed couldn't drain its reserves where one third of roughly 4 trillion reserves are accounted for mortgage backed securities
The Fed must be forced to buy junk bonds later on if they keep draining liquidities in the sp500."

That is goldbug logic at work. First, we are told that there is excess liquidity in the system that the FED could not eliminate through the sell of mortgage backed securities, and then that the FED may be soon forced to inject extra liquidity into it through the purchase of junk bonds.