Governments have outlawed the use of old currencies in the past. Why would the US not be able to the same? They do not need to take out of circulation; all they have to do is say it is no longer legal tender. Or, they can just do as they have been, keep “printing” more and more of it making your cash worth less and less. A few years ago, I looked into how much $10,000 in 1970 was worth in the years I checked, around 2017, it was something like $68,000. If there was something I wanted that cost $10,000 in 1970, I would have to $68,000 for in it 2017. With the “printing press” cranking out dollars like a sailor on shore liberty drinks beer these past few years, this is probably an even bigger problem. Using certain non cash methods of payment requires ID and sometimes other documentation. What could they not put the same requirement on cash transactions? They do in Japan for some cash transactions. The US can do it too. We need to fight this, not try hiding from it.