A cashier costs more than a self-checkout per transaction. However, a self-checkout costs far more upfront than a cashier.
A cashier is an active theft of product deterrent and will save the company money in the long run, whereas a self-checkout expects the customer to be honest. Not all customers are but then not all cashiers are either.
Customers like the human approach and prefer a live person over a machine, however, when line-ups occur people tend to opt for the faster way out of the store and some believe that involves serving themselves.
Self-checkouts don't offer discounts or rebates for using them and saving the company money, but then, in many stores, humans tend to slow down the process of harassing customers with things like credit card offers and discount card enrolments.
In many instances, retailers are turning to self-checkouts not because they are cheaper but because they just can't find the labour. $14/hr or $20/hr fewer people these days want to be cashiers. Don't think so? How many people on unemployment rush out to get a job working in retail as a cashier just to get off EI. Many will opt for drawing EI over standing on their feet most of the day dealing with irritated people who wonder why the store stopped giving out rainchecks in 2004.
As for the retail stores getting them because the government raises the minimum wage - sorry, that's false. While it seems to correspond with wage increases self-checkouts in retail stores have been in place for a couple years now, long before minimum wage made its a recent jump. Self-checkouts first became popular as line busters, reducing long line ups and opting people to choose their own speed at which they leave the store.
People like convenience, self serve banking, self serve gas pumps, and self serve pop machines in retail stores that sell an aisle full of every pop/soda you can imagine. People like convenience and in a time of online shopping and mobile banking people want their checkouts to be as fast as their smartphones.
However, what retailers didn't understand is that many people also like human interaction and some being able to talk to another person as they leave the store.
In the end, if you want stores to stop installing self-checkouts you have to do one of two things.
1) stop using them, and,
2) teach your kids it's okay to be a simple cashier if it means providing for your family.and paying your own way in life.
Who am I? Well, I've been in retail for over 30 years now so, while I'm no expert, I do know a thing or two.