A problem not yet mentioned here is the spread of bacteria through reusable plastic bags. A few years ago there was a study where the researcher contaminated a bag with a virus that was harmful to humans and gauged its transmission around the store. It ended up pretty much everywhere. Washing reusable bags pretty much destroys bacteria and viruses, but not many people do that regularly (myself included).
A woman in front of me at the grocery checkout had the nastiest reusable bags. I put my groceries back in the cart and went to another checkout. Sure, all the cashiers have dirty hands but geez.
Why waste good water, soap and electricity to clean plastic bags?