What's an example of good people doing good things, which is not an act of harm reduction or mitigating some kind of evil?

It's basically a shorthand way to see if someone is good. Not returning a cart is no illegal nor a big inconvenience. Returning the cart brings no reward but is the right thing to do. In the absence of reward or societal pressure to return a carr, only the truly good will.

https://www.nytimes.com/2021/06/08/style/shopping-cart-parking-lot.html