It doesn't, it's because people shoplift at self checkout all the time and the big retailers can't figure out how to stop it. Almost every shop in my town forces you to do self checkout, they don't even have cashiers most of the time. Last time I was at my local walmart they had like 6 self checkouts and 4 cashiers just standing there staring at everyone trying to find shoplifters. They still can't find them though lol.

I respect your preference, and for some people it could even be considered a "reasonable accommodation."

But I prefer to have the person who does this all day whip through the scanning and bagging while I pay up. It may not be rocket surgery, but good cashiers have an efficiency of eye/brain/hand motion that I can't match. Especially when there's multiples of the same item, their machine trusts them to do it the efficient way rather than scanning and weighing each item. Or having the produce codes at their fingertips without stopping to read them. And since all machines have little quirks, it's helpful to know exactly where to apply "percussive maintenance."

I am comfortable speaking with strangers, so I always thank them and wish them a good day. And I don't stand for entitled assholes giving them shit, either.

Having both options is best and should be part of ADA compliance.

Yea the issue is the employer doing it to make more profit instead of spreading the more profit they make to the workers. There is nothing wrong with self check out. There is something wrong with people being paid shit when the company is sending dividends to stockholders instead.