Once we (society) are entirely dependent on virtual money - which is what we are talking about here - we will potentially be completely at the mercy of the powers-that-be at any given moment, not just those of our own country, but worldwide.
Can you magine how that could be used against citizens who are even suspected of plotting against their leaders under all but the most liberal of governments?
Imagine a war situation, where there is an invasion - again, the aggressor will have everyone by the virtual purse-strings.
Then there is the huge and very real danger of cyber attack, where a foreign power brings the whole electronic system of its 'enemies' tumbling down, causing utter chaos.
No one can buy anything, partly because they have lost access to their virtual money, but also because almost everything that would be bought with that virtual money is also unavailable because the systems that make /distribute necessities are all computerized and hit by the same attack.
Blimey, it has caused people enough problems when just one bank has a temporary glitch, leaving customers unable to pay bills or get real money for a few days, or even hours, but that is nothing to what could, and quite likely will happen at some stage.
I suppose I will be accused of being melodramatic - maybe I am. Who knows!.
I know these things might sound out of place on a thread about preferences between cash and card, but we are going so quickly now in the direction of a cashless society that these things are already genuine dangers and need to be thought about, taken into consideration before we sleepwalk into a totally cashless world.