I have a clip from my dashcam floating around somewhere of me stopping, jumping out of my car, then hauling ass to catch someone's runaway cart moments before it hit a parked car. Honestly one of my proudest moments.

On the opposite end, I once left a cart (on a curb) and it haunted me. To be fair, it was absolutely storming outside and I was chilled to the bone and just wanted to warm up..

1. I used to work at a supermarket and preferred returning carts to other tasks, and got paid hourly. When someone returns the cart, they're doing that hourly work for the store owner for free. Since time is rival, you could be more effective with your altruism than helping store owners.
2. You're depressed because there's so much homelessness, right?