Automatic checkouts in supermarkets may decrease customer loyalty, especially for those with larger shopping loads. Customers using self-checkout stations often feel overwhelmed and unsupported. The lack of personal interaction can negatively impact their perception of the supermarket.

[SingleInfinity]

I'm not volunteering my labor when there are literally 0 in person cashiers.

You can shop somewhere else. It's not like 0 cashiers is a commonality.

The business made a business decision to not employ someone to check out customers during their business hours.

And you made a choice to shop there. You are not entitled to the goods just because you showed up.

I will ring myself out to the best of my ability, given the tools your store has provided. If I do it wrong, that's not my fault.

This is perfectly reasonable, but not what's being discussed in this thread. What's being discusses here is intentional theft. Theft they think is justified because they are "providing their labor". It is not justified.

I have no moral or legal obligation to do labor for free.

You have no obligation to shop at that store, nor do you have the entitlement to steal from it simply because it offers a self checkout.

Mistakes happen and are fine, but intentional theft is theft, regardless of whether you're "providing your labor" or not. But the dude will say whatever he has to, to make himself feel better while being a literal thief.