Cash is King/Queen; great for tax payment suppression; privacy; etc.
If people want the convenience of paying by credit/debit card they should be able to do so and merchants should be permitted to pass ONLY the ACTUAL COSTS on to the user. In some jurisdictions Mastercard, Visa (and Uncle Tom Cobley) write in to their contracts that no price differential between card users and cash payers is permitted which means that cash people get short-changed.
Cards have real drawbacks. An error by a bank (Hello, HSBC) can deprive a debit (or credit) card user to accessing their account even though in good standing. The FBI (and Plod) can receive real time reports on card usage (this is achieved by lowering the credit limit to zero for the card requiring phone approval every time)..
'Authorities' can gain access for all manner of 'reasons' be they unrelated criminal matters, tax related matters or any point in time or physical place.
Lawyers acting in civil matters can also, with court orders, access data. Might be embarrassing in divorce matters. Use a card for a flight and your data will go viral to every country on your itinerary; the data will be held on GDS all with computers in the U.S. which under 'The Patriot Act' (sic) can be accessed without warrant.
The card companies use your usage data for all manner of purposes including onward selling of data.
Of course not everything is bad with cards: you don't need cash and you can 'stop payment'.
Cash can't be traced; leaves no 'bit' trail, honoured by most vendors and is great for avoiding tax!