Earlier quoted context omitted.
I think you should have to take a simple intelligence test as you walk into a store. If you refuse or fail you don't get to use the self checkout. This should be a very very simple test like being able to read a number properly and pick something out of a list....when I stand there watching people use those machines I really feel like 90% of them would fail.
That's right, it's the users who are stupid, and not the designers who didn't focus enough on the UX.
When it comes to technology, some people have realized that screaming for help and blaming the system is an option, and seem to always pick that over reading a simple instructional sentence presented in bright colors directly on screen.
If you've ever been "the family tech guy/girl", then you likely have experienced this or understand.