Why do you think they're useless? They certainly aren't currently [1]. Someone has to do their work, either paid employees or unpaid volunteers (i.e. customers).
[1] at least until that Amazon fantasy-land store becomes a practical reality, if it ever does
Half the cashier's job is automated (tallying is managed by scanning in the items, payment is handled by using the customer facing CC machine; they only handle cash, checks, and manual entry of produce). Bagging is often handled by cashiers, customers, or dedicated baggers. Baggers are cheap, the only skill required is to know not to put eggs beneath a half-gallon of milk (though many seem not to know this anymore). Cashiers cost more because you have to trust them.
Handling cash can be handled by automatic machines (as evidenced by the many self-checkout systems) with one person dedicated to 4-8 checkout stations to assist with issues, check customer IDs, etc.
It's not that they're useless, but cashiers' utility is greatly diminished these days with automation reducing the skill, trust, and number of personnel required.
This is what I think most people miss when they criticize automation. It's not that an android-looking robot will come and stand in your spot and do your job, it's that automation makes one person more effective, and able to do the job of multiple people.
The supermarket I go to recently got rid of all of its self checkout lines and replaced them with additional express (15 item or less) lines. I'm not sure their reasoning for it but I don't think cashier automation is a sure thing.
Your point is spot on but only disproves the likelihood of any coming calamity. Understood in the way you describe, automation making human labor input redundant has been pervasive and relentlessly constant for at least 100 years. This sort of technological progress is precisely what accounts for improved economic productivity.
Interestingly, productivity has plateaued these past few years at the same time we're supposedly entering a golden period for applied machine learning. There are a million ways to explain that away, of course, but it's a reality people should really consider carefully before reflexively dismissing as transient.
In any event, if productivity improvements were to kick into high gear tomorrow we could expect more of the same--increasing displacement but not an overall, calamitous reduction in jobs per se. The increase in the unemployed labor force will open up new opportunities for businesses built around human services, while the reduction in prices for consumer goods will allow people to spend more money on those new services.
Things can totally get worse, especially in terms of wage inequality. But the laws of supply & demand make it almost impossible for a complex labor economy to simply fall off a cliff in the ways that overly imaginative "futurists" and "thinkers" would have us believe. In terms of basic economics, nothing about machine learning is substantially different from historical disruptions.
If you were to teleport somebody from 100 years ago to today, and then to 20 years from now, the relative differences in automation and computer intelligence between today and 20 years in the future would likely be indistinguishable from his perspective when comparing either of those time periods to 100 years ago. And yet without a doubt the contemporary and future economies would be far stronger, wealthier, and even more "equal" compared to the time period he came from. All precisely _because_ of that automation, not despite it.
Why do you think they're useless? They certainly aren't currently [1]. Someone has to do their work, either paid employees or unpaid volunteers (i.e. customers).
[1] at least until that Amazon fantasy-land store becomes a practical reality, if it ever does
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