First of all, thank you for replying. There's probably many on the subject who would down vote a counter point without even reading, let alone replying.

it opens up the "well since he put the cart wherever he wanted I can do the same" mindset

This seems to make multiple incorrect assumptions:

1. there's not already multiple carts that could inspire that mindset. There's usually many out of place for much longer. This cart was literally there for less than 15 seconds.
2. people are biased towards replicating negative behavior. As I said, I grabbed the cart on my way in, but that won't inspiring order the way leaving it inspires chaos?
3. most people are unable to differentiate between where a cart is easy to grab and where it's just going to linger or get in the way. I know I'm not the only one grabbing carts on my way in. It doesn't take years of cart collecting to notice.

I feel depressed when I see assumptions that seem to view people as really dumb and requiring hard-line, no-exceptions rules. It gets uncomfortably close to an authoritarian worldview. I wrote my previous reply because, while I believe people should put their carts back, and model that behavior myself, I also believe things are rarely black and white and it's valuable to interrogate when that might be.

Edit: add opening thanks