I know some people think that self-checkout is making the customer do the cashier work for free, but honestly, having experienced it both ways, I'd much rather do it myself. It's not like I am doing anything else at the time, and shopping already involves something very similar, regardless.
I imagine that if grocery stores had started with each person having a personal shopper who picked things off the shelves and pushed the cart around, then if some stores started making people push their carts around themselves, you'd hear the same complaints.
But I am already picking up each item, one by one, when I put them into the cart. To me, it's really not that different to pick up the items one by one, scan them, and put them into the bag.