I'm having a tough time imagining a scenario where you're in too much of a hurry to spend 30 seconds returning the cart, but not too much of a hurry to buy your merchandise and load it in your vehicle.

If you are in such a hurry you don't even have 30 seconds, you shouldn't be shopping in the first place, especially if you buy enough to fill a cart.

Unless you get a phone call just after unloading your shit into your car what sort of emergency allows you to shop but still demands literally no second be spared?

Believe it or not, jail!

I suppose if it was dire you save those 30s, it's acceptable.

But you would not be immune to being judged by a third party. They wouldn't know the situation is dire unless explaining it, which would take at least a few seconds.

Walmart sells indulgences.

The description says unless it's a dire emergency

The post specifies an exemption for dire emergencies. It would need to be pretty dire for 30s to make a meaningful difference.

Otherwise, by the metric here, you're a bad person whenever you're in a moderate hurry.