I realize you probably don't hold this position, but legality aside, that argument falls flat on its face when you consider the value of your time vs the value of items you're stealing. Self-checking out groceries takes maybe 3 minutes for a full cart? Suppose the store would have otherwise needed to hire a cashier earning $20/hr. Let's double that to account for other expenses like payroll taxes and insurance. $40/hr for 3 minutes works out to $2. That entitles you to a free candy bar, not ringing up a pack of steaks as bananas.
>Basically "if you don't want me to steal, then hire someone to watch me".
At the risk of being called a "corpo bootlicker" or whatever, this is basically along the same lines as "if you don't want me to grope you, don't dress provocatively".