Also if they gave a shit, they'd have staff on all checkouts and not use self-service checkouts. Staff are more expensive.They know; they just don't care.
While I agree that the stores "deserve" the amount of the theft through fraud that comes with replacing human checkers with automated checkout systems, that doesn't make your behavior in explicitly taking committing that fraud any more ethical.
Scan something wrong by accident, that's the store's fault for setting up the system to allow such accidents. But to intentionally exploit their system, that's on you.
I personally make it a rule to never go through automated check-outs because I think the stores that use them are not holding up their end of the social contract. I've even abandoned a few carts when I got to the check-out and found they had no human checkers (I found out the hard way that some grocery stores around here go 100% automated after 10pm).