I think if you're going to go through the trouble to return your cart to the cart area then yeah, slot that bad boy into the stack the way it's supposed to go. Otherwise it's like those people who pick up their dog's poop and just hang the bag on a tree branch for someone else to put in the trash. Either do the thing, or don't do the thing. Doing it halfway just makes a different kind of mess.

I found out a new (new to me at least) bit of cart-return etiquette last year when I was using the handicap parking spaces for a couple months following ankle surgery. Grocery carts double as walking aids for a lot of people with mobility issues while they're at the store. Many people with those issues will purposely leave their carts in the handicap area as a courtesy for the next person with mobility issues so they can have it right away and not have to struggle all the way to the cart area. So there's at least one instance where not returning your cart doesn't make you a horrible person.