Groceries are the most low margin retail business at 1-2 percent. So the cost savings have definitely been passed on to the customer, unless you can find figures to the contrary.
If b) then we're back to where I started: you might as well complain about the discount on Swiss cheese. You don't pay more for youg goods, you may even pay less- but the store is making more money anyway.
I won't say "where is the harm in that" because there is certainly harm to the clerks- but that is a separate issue from the extreme stretching of reason to justify shoplifting in the passage I commented on.
Take the wholesale price of the product, add rent, delivery, payment processing, in store labour and all the other expenses involved in running a store, then add 1-2%. That gives you the price you pay in store. That formula hasn't changed since self checkout was introduced, but the cost figures have changed.
I still don't see how all this says that "the cost savings have been passed on to the customer", as per your previous comment.
I think it's more up to the supermarkets to demonstrate that self-checkout is lowering prices. As a consumer I wouldn't 'definitely' believe any cost savings would be passed onto customers, and IMO it'd be foolish to do so.