It depends on the level of competency of the executives. If the approach done with low frequency, feedback to upper management could trigger someone to calculate whether lost sales is worth it. If it is done on a large scale, then less competency is required for upper management to do the calculation. So the frequency of abandoned carts to have effect depends on the competency of management.

it prevents the business from functioning correctly and I think in that hypothetical scenario, you’re definitely hurting cashiers.

It’s not a boycott. You can abandon a basket in one Spar shop to send a msg then still buy the stuff at another one.

But let’s suppose it’s not just a signal but actually a boycott. To harm the cashiers the boycott would have to be on such a large scale that it causes at least one Spar shop to shut down. Do you really believe that would happen? It’s beyond unrealistic. Only 60% of the population even cares about cash. Many fewer even shop at Spar to begin with. It would be unlikely if even just 1% were to boycott on this issue. Then you have to figure that the 40% of the population who is okay with forced banking and cashless society would counter the boycott by patronising Spar when they otherwise wouldn’t. On top of that, this is not a hill Spar would die on no matter how incompetent they are. They would give in to the boycott far before closing shop.

In short, you have no chance of harming cashiers.