Every passengers has a few choices; use the app, print your own paper boarding card or pay a fee at the airport.
A ruling like this will redistribute the costs across all passengers by increasing ticket prices across the board. So everyone else gets penalised for customers who make a choice to not use modern methods or not to prepare ahead and print their own boarding card.
Pax are perfectly entitled to do their own thing, nothing wrong with that. Why should other customers have to cover for that?