My position, having worked as a checkout assistant FWIW, is the opposite. Using the self-checkout is redistributing money from the poor to the rich, AFAICT: you're saving the company wages, paying the same amount, and doing the work for free.
If the out of work checkout assistants got a living wage then you might be on to something.
However, checkout assistants are not very well paid and the job is horrible (it's not the worst, arguably, but could be improved).
I do not however feel responsible for the bad moral decisions of other people. My action in itself doesn't increase profits of the wealthy, it's actions of other people. These people need to be made socially responsible (for example via progressive taxation), not me.
It's really not even that bad, if you like talking to people. The checking groceries part can be sort of meditative and relaxing.
I prefer automated checkout too - but I'm curious as to why you think the job is "terrible"?
Before my first software development gig, I worked for 6 months as a cashier. I won't say it was all rainbows and roses, but it wasn't "terrible". Hard on the feet (standing), but I was young at the time so it wasn't too big of a deal. Dealing with irate customers could be interesting at time (pass 'em to a manager if you couldn't calm 'em down). Occasionally you'd get someone trying to return an item bought 20 years ago (actually had this happen to me).
But there were also the "regulars": The 70 year old lady who came in every Wednesday to purchase a bunch of liquor - who'd then walk out, and hop into her brand new Vette. The weird cat dude, who always smelled, but was friendly - purchasing a cart full of cat food, and another of rubbing alcohol and swabs (poor cats). The guy you always carded for beer, because he looked underage - and even though you know he wasn't, you did it anyhow, and he complained - but corporate policy, ya know?
Then a break - go face the aisles, or stock new stuff, or pull the old stuff. Have some lunch or some dinner. Eventually close the store, sweep the aisles, clean up, shut down, and go home.
For me, it was an "after school" kind of deal - not a career. But it wasn't a terrible job. Just difficult on the mind and body (it was a bit boring at times). My fellow employees were all friendly, and management was nice and helpful. I always got paid on time, meager as it was.
It gave me a better perspective and understanding for those working behind the counter, because I know what they're going thru. Plus, it also taught me how to properly scan items quickly (though when I started, the place I worked at didn't have scanners - they didn't get those until a couple of months later). Even so, when an item doesn't scan, I find it a bit frustrating, but most systems have a way still to enter the UPC number...
...still, I wouldn't want to go back to those days.
Although I take my time to go through it. Damn, if it's done by machine, I can do it on my own pace.