The point of coin-lock cart systems isn't to stop thieves. If someone's going to steal them, the carts are worth far more than the coin used.
The point of that system is to get people to BRING THE DAMNED CARTS BACK.
Instead of leaving them all over the parking lot so you have to pay someone to go out there several times a day and round them up and bring them back for others to use.
This is exactly why ALDI does it. It's also part of why ALDI's prices are so much lower than other grocery stores in my area. They're ruthless about cutting costs.
It's also why ALDI charges for bags: They're not free to the store. If you don't want to bring your own, or take some empty boxes they have lying around, then buy some.
Their stores are also set up so that the shelves can be stocked with a minimum of labor, with product generally sitting in its shipping carton with a side removed. When the carton is empty, generally a customer takes it to put their shopping in, which both uncovers the next box of product and removes a box from the store, saving the company money on labor to clean it up and also saving on disposal.
I really wish more stores did things this way. It's not as pretty as Food City or Kroger, but I don't really give a damn about how pretty the shelves look.