They might agree that they would be a better person if they returned their shopping cart. But how many would sincerely state "I won't return the cart because I don't care about putting any effort into being a good person"?
I'd bet you'd get a litany of complaints about the parking lot, the cart, the store, the weather, anything but their own decisions.
Yeah. What it boils down is "I don't want to put in even a tiny effort or suffer any inconvenience to do a simple chore that helps other people"
Which isn't something I think good people say