I always return it for a bunch of reasons.
1. It annoys the hell out of me when carts are just put anywhere, especially if it means I need to move it to park or get out of my parking spot. So I’m not about to do something that I don’t want other people doing (the old ‘do-unto-others’).
2. My parents and the Navy drummed into me the concept of ‘a place for everything and everything in its place’.
Definitely part of my upbringing! (Though it did take some time to get that one to sink in!)