Also, let's not forget that you are doing someone's job simply for using a shopping cart at all. Traditional grocers didn't have anything like the aisles we wander through now. Rather, there would basically be a warehouse with a counter at the front. You walked up with your list of items, gave it to the grocer, and they would grab the items for you. Customers gathering goods themselves didn't come about until the age of the supermarket starting in the mid 20th century.

This is also why I have zero sympathy for stores that complain about theft and shrinkage. They're the ones choosing to operate in a business model that makes theft easier. Traditional grocers didn't have to worry about shoplifting, as everything was kept behind the counter. Sure, armed robbery was a concern then as it is now, but shoplifting wasn't a concern.

When the grocery stores abandoned the traditional model, they realized the money they saved on labor would more than make up for the increased losses due to shoplifting. And that was simply a choice they made. And it's the same with self-checkout. They made a business decision that would inevitably result in increased theft, and they have no one to blame for it but themselves. If they don't like the increased theft, they can go back to cashiers. Or hell, there's nothing stopping Walmart from going all the way back to the traditional dry goods store model even. That would work really well with online orders as well. You don't even let customers wander through most of the store. You just have a very long counter at the front of the store that customers walk up and tell the workers what they want. And the workers gather the order. You either wait for them to gather it, or you place the order in advance and have it ready when you pick it up. If Walmart did this, shoplifting would become virtually impossible. Their labor costs would skyrocket, but Walmart has it in its power to completely eliminate shoplifting if they really want to.