Wrong. The correct act is to put the cart out of the way of others, but not in the corral.
You then help provide a job to a person that capitalism wants to take away. They want your free labor. And then they provide less and less corals to save those extra pennies, knowing that you'll walk. Fuck them.
Hmmmm... I am having trouble refuting this logic. Perhaps it should be viewed on case-by-case basis.
If you're done shopping and are about to leave, and you see a bunch of random carts strewn about the lot with an underpaid employee rushing around to collect them, then yeah, don't be a dick. Put the cart back.
But if the lot is already clear of carts, then maybe it does make sense to leave a cart around (in an area where it won't hit a car or something)...