When I worked in retail, lo these many, many, many moons ago, there were the sales clerks and the security folk. The sales folks often saw people stealing and would report them to security. Security would occasionally catch someone and call the cops. But most of the time they would be too late, and would then yell at us sales clerks asking why we didn't stop them. I would always answer "I'm not risking life or limb for this minimum wage job".
The Costco scan isn't security theater. It actually works, although more in favor of the customer than the store. I've actually never seen them catch a customer stealing anything, although I've seen a couple "Hey you forgot to pay for the stuff under the cart" situations. And I've definitely seen a number of catches "Hey you got double charged for this item" situations. Personally, I'm against security theater, especially the TSA, but the Costco process works.
Having said that, if you don't like it, shop somewhere else. The beauty of a free(ish) country.
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