People who predict (or currently exist) cash-free are simply those who have never had to live through some kind of natural disaster or event. Anyone who lived in NYC during Hurricanes Irene and Sandy or the major power blackout of 2003 has learned to keep a stash of cash in the house in case of complete power outages lasting days or more. Take a look at this list https://en.wikipedia.org/wiki/List_of_major_power_outages and tell me you want to rely on a plastic card (which in turn requires power and network connectivity) to buy food, petrol, or other essentials.
Biting the hand that feeds IT
