This reminds of a joke: A man bought some prunes and is eating them whole, including pits. His friend asked him: "Why don't you throw away the pits?". Man answers: "I paid by weight for the whole thing, for both flesh and pits. I am not going to throw away the things I paid for, that's wasting money"

We pay for value we get and not for the efforts of others, and for most people doing shopping, the value is in the things they buy. So if you buy the same things, you should expect the same price, self-checkout or not.

(Although there is definitely some value in the shopping experience -- a nice clean store will friendly cashiers would be able to charge more. So I can someone having "I am going to the expensive store so I don't want to do manual labor" mindset)

Isn't spending less time waiting to pay and leave the store a discount?

Very true! Thanks to lax security and apathetic employees, you can use the self-checkout to get a five-finger discount pretty easily.