Quoting ma ♥:" I know they're for safety & I'm sure the parents who use them mean well & everything... but just, ... [snip!] ... shopping cart/stroller. I don't see a reason why those few things wouldn't work so a harness is never necessary for my family."
Why those things don't work?
Jack can undo the strap in a cart and tries to leap over the side. I won't lay on my screaming child to go shopping.
Holding his hand, he does that smurffy "dead weight" thing, and I won't drag my kid through a store either.
Holding him? He arches his back and screeches, kicks, etc, to be put down.