From the interview with the Financial Repression authority podcast:
“The only way they can do that [negative interest rate policy] is to lock people’s deposits into the banking system. That is where the war on cash comes in. They would love to restrict or even abolish the use of cash within the United States if they could. That means they would have to use deposits. this is another way of propping up a very unsound and dangerously flawed banking system.”