people who have just picked up their dog's steaming pile of poo, put it in CLEAR plastic bags, and then walk along gaily swinging it like Mary Poppins.
They should stuff it in their pocket. At least then I'd be spared the sight of it, AND it'd keep their hand warm.
It's to show they really have picked up their dog's Posh. If they use an opaque bag, they may just be carrying random rubbish whilst leaving the Posh to add to the excitement for pedestrians trying to negotiate ice-covered pavements.