True, but having a cashier standing there waiting to scan your items will prevent most normal people from stealing. Sure, some will brazenly walk right past with a TV on their shoulder, but most people won't.

If there's no cashier and you're doing it yourself, a whole lot more people will "forget" to scan a couple items, and that adds up.

There's usually a security person or two in the store, looking over the self checkouts. I agree that job prevents a lot of people from becoming opportunistic thiefs, but I'm making a distinction between cashiers and security. Today the store needs both.