However surely 'riding shotgun' (i.e. being there to help customers when things go wrong) on self checkouts is more interesting than mindlessly scanning items all day? (I don't know, I've done neither)

Furthermore, if there is less work to be done in supermarkets, then people can spend more time doing more interesting/productive work or simply enjoying their leisure. The issue is not that this (or any) automation is destroying people's livelihoods, but that the value added is being predominately captured by the already wealthy.

Portugal does suffer from an excess of 'work is for the workers' mindset, which is part of the reason it is so poor (compared to other Western European countries).