Tipping used to be a way to implement a truly granular free market (or however you want to justify it, that's besides the point). Point being is, it's how service workers largely get paid. So regardless of how we got here, to not tip them is to not pay them fairly for their work. The problem now is that commerces turn tipping on by default at point of sale devices indiscriminately. So tipping when you see the screen is poor advise as it just gives into greed and manipulation. Follow the original rule: you tip when there is personalised service rendered, for example restaurant waiter, or driver, or barber or hair dresser. If it is neither personalised, nor a service rendered by an individual, you never tip.