Sure, you're right. It's a not a 1:1 trade. But if you're working at a company that produces checkout machines, and America goes on this massive boycott of the machines and you get laid off, it doesn't really matter to you whether it's a 1:1 trade. You're not a bad person for building machines that are replacing cashiers, you needed the money to feed your family. The same goes for the cashiers. You need a job. The production worker's needs aren't your concern, you need money to live. Are either of these people less important than the other?

Things change. Sometimes the changes are harsh, but over time society adapts. Yes, cashier jobs may be lost, but those cashiers will move into other things over time. Will it be easy for them? Probably not. But it's never been easy for the working class, and it never will be. A farm that used to need 50 people to operate now needs 5. Where did all those farmhands go? What about milkmen? Elevator operators? Street car drivers? Telegraph operators? We should have 50% unemployment because all those jobs disappeared and were never replaced, right? But that's not the case. Those jobs returned in other forms in other industries.

This idea of refusing to change is only going to hinder those cashiers in the end. The change cannot be stopped. Businesses will take the path that makes them the most money and that's that. The only thing you can do for the cashiers is help them realize that their trade is dying so they can begin taking steps to move into other things while they still can. I'm really sorry, but you refusing to use checkout machines isn't going to help them. If you really want to make a difference, encourage people you know who work as checkout clerks to start thinking of some other things they might want to do.