For someone who is supposed to be intelligent this proposal sounds dangerously inept. They start from the premise that only bad people use $100 bills w/o providing any evidence the claim is true. Incredibly they then use that to support their thesis that both $20, and $50 bills should be phased out as well.

The assumption that a cashless society would give a central bank more control by making negative interest rates viable is also totally nuts. People would just end up buying things like precious metals, low inflation crypto currencies or anything else that emerged as a defacto store of value. In Baltimore for example there is a strong underground market for name brand laundry detergent and as a result you can barter a jug of it for drugs.

http://nymag.com/news/features/tide-detergent-drugs-2013-1/