In California you run the cart up a curb, leave it in an empty parking space, or maybe give it a gentle push and let it roam free. Corrals are depots for broken and rusted carts.
I really hate trying to turn into a spot that's flanked by two SUVs only to find a cart in the way. People are incredibly lazy. I love the ALDI's quarter scheme… it's just enough of a nudge to get people to do the decent thing.
What you were told sounds like one of those slightly tongue-in-cheek excuses people sometimes use to justify behavior, though that doesn't necessarily make it insincere. For most of high school I worked dishwashing jobs. A typical task for a dishwasher includes picking up trash in the parking lot. People throwing trash in the parking lot weren't doing me or anyone else any favors.
Do you do that consistently now that you're an adult? Do you bus your own tables at local restaurants (small business owner) but not at franchise restaurants?