Just like the shopping cart theory itself, this is mostly just a thought experiment at this point in time.
The point of a protestation is to make it hard for others to ignore, and make it clear what the end condition is. I don’t plan on just starting to do this as an individual because it would have no impact; I still make sure my own carts get returned personally.
The point stands that our goodwill is frequently exploited for profit, often under the pretense that it’s just basic human decency.